WO1998028067A1

WO1998028067A1 - Apparatus and methods for wetting or flushing filters

Info

Publication number: WO1998028067A1
Application number: PCT/US1997/023525
Authority: WO
Inventors: Jun Naitou; Stephen A. Geibel; Nobuyuki Mori
Original assignee: Pall Corporation
Priority date: 1996-12-20
Filing date: 1997-12-22
Publication date: 1998-07-02
Also published as: JPH10192663A

Abstract

A filter wetting or flushing apparatus (10) according to one aspect of the invention comprises a syringe (11) having a cylinder (13) and a piston (14), a liquid inlet (15) and a liquid outlet (16), and a valve assembly (20, 21). The liquid inlet and the liquid outlet are in fluid communication with the barrel space (17) of the cylinder. The valve assembly allows liquid flow from the liquid inlet to the cylinder but blocks reverse liquid flow, and allows liquid flow from the cylinder to the liquid outlet but blocks reverse liquid flow. The liquid inlet is adapted to be connectable to a port (2) of a filter (1) to draw a liquid (3) through the filter into the suction port. An apparatus (80) for wetting or flushing a filter (85) according to another aspect of the invention comprises a pump (81) that includes a suction port (82) and a pressure port (83). The suction port is adapted to be connectable to a port (84) of a filter (85) to draw a liquid (86) through the filter into the suction port.

Description

APPARATUS AND METHODS FOR WETTING OR FLUSHING

FILTERS

This application claims the priority of Japanese application 341803/96, filed December 20, 1996, which is incorporated by reference in its entirety.

Technical Field

This invention relates to apparatus and methods for wetting or flushing a filter.

Background of the Invention

A filter made of a microporous membrane of a hydrophobic material such as tetrafluoro-resins has been widely used in the filtration of liquid. When such a filter is used in a filtration line using a high surface tension liquid such as pure water, it needs to be sufficiently wetted. Wetting (or prewetting) a filter generally includes introducing a liquid with low surface tension such as alcohol into the filter medium and then replacing the liquid with low surface tension with a liquid with high surface tension. Without prewetting treatment, an aqueous liquid such as pure water used for washing semiconductor products can not be passed through the filter medium due to the hydrophobicity of the membrane, or a very high pressure may be required. If the prewetting treatment is insufficient and the filter is not fully wetted, air locks may still occur and the filtrate may not be passed through the filter efficiently. If the prewetting treatment is omitted or insufficient, the air remaining in the filter may enter the filtrate during filtration operation. Any air bubbles in the liquid may have a detrimental effect on the quality of the products when the filter is used to filter feed liquid such as a resist solution in a semiconductor manufacture line .

A prior method for prewetting a filter includes immersing the filter in a vessel filled with alcohol or the like to sufficiently wet the filter, then transferring the filter to a vessel filled with water to replace the wetting liquid remaining in the filter with water (immersion method) . However, this method is inefficient because prewetting and water replacement take a long time. In order to solve this problem, a method for rapidly prewetting a filter under high pressure by placing the filter in a pressure vessel containing water was proposed, as disclosed in JP-A-135423/91, for example. However, this method requires equipment for treating a filter under high pressure, thus involving a large-scale system. When a filter is used in a semiconductor manufacturing line, it is undesirable to introduce such a large-scale system in a clean room for manufacturing semiconductors. Another solution was an apparatus for prewetting a filter by placing a filter in the pressure line of a pump to forcibly circulate a wetting liquid such as alcohol under pressure (pressurization method) . A disadvantage of this method is that when used to wet a capsule-type filter, the wetting liquid may damage the filter medium because it flows from the secondary side to the primary side of the filter.

Yet another solution was to package a prewetted filter in a wet state and distribute it as a filter product in order to avoid prewetting the filter at the location where the filter is being used, but this method involves the following problems: the wetting liquid may leak from the packaging container or may deteriorate due to the proliferation of bacteria or the like during storage; some kind of wetting liquid may generate a gas during storage to rupture the package or to emit a toxic gas when the package is opened.

Summary of the Invention An object of this invention is to solve the problems associated with these prior filter wetting apparatus. Further, an object of some aspects of the invention is to provide a filter wetting or flushing apparatus and/or method which can easily prewet or flush a filter without the necessity of installing a large system. Still further, an object of some aspects of the invention is to provide a filter wetting or flushing apparatus and/or method which can be used to wet or flush a filter without damaging the filter.

An apparatus for wetting or flushing a filter according to the present invention comprises a syringe composed of a cylinder and a piston and having formed therein a liquid inlet communicated with the barrel space of the cylinder through a liquid inlet passage and a liquid outlet communicated with the barrel space through a liquid outlet passage; and an attachment, one end of which is so constructed that it is removably engaged with said liquid inlet of said syringe, another end of which is so constructed that it is removably engaged with the opening of the filter to be prewetted, which has a liquid passage communicating said both ends formed therein; characterized in that a check valve allowing liquid flow from said liquid inlet to said barrel space of said cylinder but checking reverse liquid flow is provided in said liquid inlet passage in said syringe, and a check valve allowing the liquid flow from said barrel space of said cylinder to said liquid outlet but checking reverse liquid flow is provided in said liquid outlet passage in said syringe.

Another apparatus for wetting or flushing a filter according to the present invention comprises a syringe including a cylinder and a piston disposed in the cylinder, a liquid inlet and a liquid outlet each in fluid communication with the barrel space of the cylinder, and a valve assembly which is coupled to the inlet and the outlet to allow liquid flow from the liquid inlet to the barrel space of the cylinder but block reverse liquid flow, and to allow the liquid flow from the barrel space of the cylinder to the liquid outlet but block reverse liquid flow. The liquid inlet is adapted to be connectable to a port of a filter to draw a liquid through the filter into the liquid inlet. Yet another apparatus for wetting or flushing a filter according to the present invention comprises a dual action syringe which includes a cylinder and a piston which is disposed in the cylinder and divides the barrel space of the cylinder into two chambers, a liquid inlet and a liquid outlet each in fluid communication with the two chambers of the cylinder, and a valve assembly which is coupled to the inlet and the outlet and allows liquid flow from the liquid inlet to the two chambers of the cylinder but blocks reverse liquid flow, and allows the liquid flow from the two chambers of the cylinder to the liquid outlet but blocks reverse liquid flow. The liquid inlet is adapted to be connectable to a port of a filter to draw liquid through the filter into the liquid inlet.

A further apparatus for wetting or flushing a filter according to the present invention comprises a pump which has a suction port and a pressure port. The suction port is adapted to be connectable to a port of a filter to draw a liquid through the filter into the suction port. A still further apparatus for wetting a filter comprises a pump which provides a liquid flow through the filter, a prime mover which is coupled to the pump to power the pump, and an automatic control device which is operatively associated with the prime mover and includes a sensor sensing directly or indirectly the wetness of the filter. The automatic control device stops the liquid flow through the filter when the filter is sufficiently wetted. A yet further apparatus for wetting or flushing a filter comprises a pump which provides a liquid flow through the filter, a prime mover coupled to the pump to power the pump, and an automatic control device which is operatively associated with the prime mover and includes a pressure sensor sensing the pressure difference across the filter. The automatic control device stops the liquid flow through the filter when the pressure difference reaches a predetermined value.

A method for wetting or flushing a filter according to the present invention comprises drawing a fluid through the filter into a suction port of a pump.

Brief Description of the Drawings

Fig. 1 shows a concept of a wetting or flushing treatment of a filter using a filter wetting or flushing apparatus according to one embodiment of the present invention.

Fig. 2 shows a concept of a wetting or flushing treatment of a filter using a filter wetting or flushing apparatus according to another embodiment of this invention.

Fig. 3 shows a concept of a wetting or flushing treatment of a filter using a filter wetting or flushing apparatus according to yet another embodiment of this invention.

Fig. 4 shows a concept of a wetting or flushing treatment of a filter using a filter wetting or flushing apparatus according to still yet another embodiment of this invention. Fig. 5 shows an apparatus used in Example and

Comparative examples to determine pressure loss values of the filters prewetted. Fig. 6 is a graph showing relationships between the flow rate and the pressure loss characteristics of the filters prewetted in Example and Comparative examples . Fig. 7 is shows a concept of a wetting or flushing treatment of a filter using a filter wetting or flushing apparatus according to yet another embodiment of the present invention.

Fig. 8 shows a concept of a wetting or flushing treatment of a filter using a filter wetting or flushing apparatus according to a further embodiment of this invention.

Fig. 9a shows an attachment used in a filter wetting or flushing apparatus according to an embodiment of this invention.

Fig. 9b shows another attachment used in a filter wetting or flushing apparatus according to an embodiment of this invention.

Description of Preferred Embodiments

To avoid repetition, this section only describes the embodiments of the invention as wetting apparatus and their operation in terms of wetting a filter. The apparatus and the methods however can also be used to flush a filter by drawing a liquid through the after it has been used in a filtration line.

According to one aspect of the invention, referring to Fig. 1, a filter wetting apparatus 10 may comprise a syringe 11 and an attachment 12. The syringe 11 is composed of a cylinder 13 and a piston 14 which is disposed in the cylinder 13, and includes a liquid inlet 15 at the forward end of the cylinder 13 and a liquid outlet 16 on the lateral side of the cylinder 13, as shown in Fig. 1, although the liquid inlet 15 and the liquid outlet 16 may be placed at any convenient locations on the syringe 11. The liquid inlet 15 may communicate with a barrel space 17 of the cylinder 13 through a liquid inlet passage 18, and the liquid outlet 16 may communicate with the barrel space 17 of the cylinder 13 through a liquid outlet passage 19 although the liquid inlet 15 and the liquid outlet 16 may communicate directly with the barrel space 17 without the passages 18, 19. Preferably a check valve 20 is provided in the liquid inlet passage 18 to permit a liquid flow from the liquid inlet 15 to the barrel space 17 of the cylinder 13 but block a liquid flow in the opposite direction, and another check valve 21 is provided in the liquid outlet passage 19 to permit a liquid flow from the barrel space 17 of the cylinder 13 to the liquid outlet 16 but block a liquid flow in the opposite direction. The check valves 20, 21 may be a separate assembly, or they may be an integral or unitary part of the syringe 11 or of the attachment 12. Alternatively, a spool valve (not shown) disposed between the barrel space 17 and the liquid inlet and outlet 15, 16 may be used to perform the functions of the check valves 20, 21. The position of the spool valve may be controlled by the pressure in the barrel space 17 of the cylinder 13 and the openings of the spool valve direct fluid flow between the barrel space 17 of the cylinder 13 and the liquid inlet and outlet 15, 16. The attachment 12 may be attached to the liquid inlet 15 of the syringe 11. The attachment 12 has one end 21 adapted to engage the liquid inlet 15 and another end 22 adapted to be connectable to a port 12 of the filter 1 to draw a liquid through the filter 1 into the cylinder 13. In the preferred embodiment shown in Fig. 1, the attachment 12 is inserted into the filter 1 and the syringe 11. Seals are provided by placing O-ring seals in the grooves on the inside circumferences of the syringe 11 and the filter 1. Alternatively, either or both of the syringe and the filter may be inserted or threaded into the attachment or may be directly or indirectly attached to the attachment in any other suitable way, including, for example, by means of a bayonet fitting. Seals may also be provided by flat gaskets or, if threads are used, by placing plastic sealing tapes such as PTFE thin strips on the threads . The ends 21, 22 of the attachment 12 may communicate with each other through a liquid channel 23 formed in the attachment 12. The structure of a connecting part between the attachment and the syringe is such that, once the attachment 12 is fitted to the liquid inlet 15 of the syringe 11, an end 21 of the liquid channel 23 of the attachment 12 is connected to the liquid inlet 15 of the syringe 11 to establish a liquid-communication between the liquid channel 23 and the liquid inlet passage 18. However, the attachment 12 may not be needed, and the forward end of the cylinder body 12 including the liquid inlet 15 may be adapted to be directly connectable to a port of a filter to draw a liquid through the filter into the cylinder. If many different types of filters are used in a production line, a plurality of attachments may be used, each adapted for use with different types of filter and the same or a different syringe. Alternatively, an attachment may be configured to receive a plurality of filters simultaneously, and thus a syringe may be used to simultaneously wet a plurality of filters.

The end of the attachment 12 or the syringe 11, which is adapted to be connectable to a filter, may be configured to be connectable to more than one type of filter. For example, as shown in Fig. 9a, the end of syringe 11 is configured to be insertable into three types of filters 4, 5, 6, each type having a different port size. Alternatively, as shown in Fig. 9b, the end of the syringe 11 may be configured to be insertable into one or more types of filters 8 and/or to be capable of having one or more types of filters 7 inserted into it. To the liquid outlet 16 of the syringe 11 may be connected a liquid outlet tube 24 which is normally formed to be suspended downward when the filter 1 is prewetted (i.e. when the syringe 11 is oriented downward) . Preferably the liquid discharged from the outlet 16 is returned to the vessel although it may be discharged to any other place such as another vessel.

The filter 1 to be prewetted by the filter prewetting apparatuses and methods according to the present invention may be, for example, a cylindrical cartridge-type filter formed of a hydrophobic microporous membrane of a fluororesin or the like pleated with a support and drainage material into a cylinder having one end sealed and the other end opened, although a filter prewetting apparatus embodying the present invention may be used to prewet filters of any configurations, including, for example, filters of cylindrical or flat configuration, with pleats or without pleats, or of open or dead end, and/or filters of different filter media. A capsule-type filter receiving such a filter cartridge in a housing may also be prewetted according to this invention.

In addition to the syringe 11 shown in Fig. 1, other types of syringes such as a dual action syringe may be used to draw a liquid through the filter. For example, an apparatus for wetting a filter according to the present invention may use the dual action syringe 60 shown in Fig. 7. The dual action syringe 60 comprises a cylinder 61 and a piston 62 disposed within the cylinder 61. Preferably the piston 62 sealingly engages the inner wall 63 of the cylinder 61 and divides the inner space of the cylinder 61 into two separate chambers 64, 65. Each of the chambers 64, 65 may be connected to a pair of check valves 66, 67, 68, 69 which may provide functions similar to those provided by the check valves 20, 21 shown in Fig. 1. For example, the check valves 68, 69 may permit liquid flow from the liquid inlet 70 to the chambers 64, 65, respectively, but block liquid flow in the opposite direction, and the check valves 66, 67 may permit liquid flow from the two chambers 65, 64, respectively, to the liquid outlet 71 but block liquid flow in the opposite direction. Alternatively, a spool valve (not shown) may be provided to perform the functions of the check valves 66, 67, 68, 69. The position of the spool valve may be controlled by the pressures in the two chambers 64, 65, and the openings of the spool valve direct fluid flow between the two chambers 64, 65 of the cylinder 61 and the liquid inlet and outlet 70, 71. The check valves 66, 67, 68, 69 or the spool valve may be a separate assembly, or they may be an integral or unitary part of the syringe 60 or of the attachment 72. The liquid inlet 70 may be adapted to be directly connectable or indirectly connectable through the attachment 72, to a port of a filter to draw a liquid through the filter into the liquid inlet 70. The two chambers 64, 65 may be used solely or jointly to draw liquid through the filter. One of the advantages of the dual action syringe is that its flow capacity is almost twice that of a single action syringe of the same physical size.

According to another aspect of the invention, a method of wetting a filter includes directly attaching a liquid inlet of a syringe to a port of a filter to draw a liquid through the filter into the liquid inlet, or alternatively, indirectly attaching a liquid inlet of a syringe to a port of a filter via an attachment to draw a liquid through the filter into the liquid inlet. For example, referring to Fig. 1, the opening 2 of the filter 1 may be directly attached to the liquid inlet 15 of the syringe 11, or the opening 2 may be indirectly attached to the inlet 15 of the syringe 11 via the attachment 12. If the attachment 12 is used, one end 21 of the attachment may be fitted into the liquid inlet 15 of the syringe 11 and the other end 22 of the attachment 12 is fitted into the port 2 of the filter 1. In this state, a secondary space of the filter 1 (barrel space of the cylindrical filter) and the liquid channel 23 of the attachment 12 and the liquid inlet passage 18 of the syringe 11 communicate with each other. After the filter 1 is attached to the inlet 15 of the syringe 11, either directly or indirectly, the filter 1 may be completely immersed into a liquid 3 in a vessel (see Fig. 1) . When the piston 14 is pulled up in this state, the liquid 3 is passed through the filter 1 and sucked into the cylinder 13. When the piston 14 is pushed down, the liquid in the cylinder 13 is discharged through the liquid outlet 16, and returned to the liquid vessel. Here, the liquid can not be returned to the secondary side of the filter 1 through the liquid inlet 15 in the presence of the check valve 20 which permits only a flow from the liquid inlet 15 to the barrel space 17 of the cylinder 13 but blocks a back flow. The liquid or air can not be returned to the cylinder 13 through the liquid outlet 16 during the pulling-up operation of the piston 14 in the presence of the check valve 21 which permits only a flow from the barrel space 17 of the cylinder 13 to the liquid outlet 16 but blocks a back flow. As a result, the liquid is circulated through the filter 1 by repeating the reciprocating motion of the piston 14 for several cycles, whereby the filter 1 is completely wetted with the liquid and the air in the filter is removed from the liquid outlet tube 24 to the outside of the system.

When the filter fitted to the apparatus of this invention is immersed into the liquid, it is preferred that the forward end of the liquid outlet tube 24 is located in the liquid as shown in Fig. 1 so as to form a closed circulation loop of the liquid, which prevents air inclusion into the filter during the prewetting operation by preventing air from entering the system from the liquid outlet tube even if some back flow occurred due to malfunction of the check valve.

If necessary, the thus prewetted filter fitted to the prewetting apparatus of this invention may be immersed into a vessel filled with water and the reciprocating motion of the piston may be repeated for several cycles in the same manner as described above to replace the liquid in the filter with water. Then the water-wetted filter may be fitted to a filtration line.

In prewetting a filter by the wetting apparatus of this invention, various liquids known in the art can be used. Representative examples of the liquid which can be used for prewetting a filter include isopropanol, ethanol, butanol, methanol, acetone, etc .

As shown in Fig. 2, a filter wetting apparatus 10 according to this invention may also be formed of an ordinary syringe 30 and an adapter 31 having one end adapted to be engaged with the forward end of the syringe. The adapter 31 may have a syringe connection port 33, a liquid inlet 34 and a liquid outlet 35. Further, the adapter 31 may have formed therein a liquid inlet passage 36 communicating between the syringe connection port 33 and the liquid inlet 34, and a liquid outlet passage 37 communicating between the syringe connection port 33 and the liquid outlet 35.

The adapter maybe arranged to connect directly to the port of a filter. Alternatively, the prewetting apparatus may include an attachment 32, one end of which is so constructed that it is removably engaged with the liquid inlet 34 of the adapter 31 and another end of which is adapted to be connectable to a port 38 of the filter 1 to draw a liquid through the filter 1 into the cylinder. The attachment 32 has a liquid passage 39 providing fluid communication between said both ends formed therein.

The prewetting apparatus may also include a valve assembly, such as a check valve allowing liquid flow from the liquid inlet 34 to the syringe connection port 33 but checking reverse liquid flow and another check valve allowing liquid flow from the syringe connection port 33 to the liquid outlet 35 but checking reverse liquid flow. The check valves may, for example, be provided in the liquid inlet passage 36 and the liquid outlet passage 37 in the adapter 31.

In the embodiment shown in Fig. 2, a desired commercially available syringe can be used to prewet a filter by appropriately designing the shape and size of the syringe connecting part of the adapter in such a manner that the syringe connecting part of the adapter may be engaged with the forward end of the desired syringe. In this case, it is preferable to provide a sealing member 40 such as O-rings at each of the connection zone between the syringe and the connecting part of the adapter and the connection zone between the liquid inlet of the adapter and the attachment in order to prevent liquid from leaking through the connection zones. It is obvious to those skilled in the art that the filter prewetting apparatus shown in Fig. 2 can also be used to prewet a filter in a manner similar to that used by the apparatus shown in Fig. 1.

Figs. 1 and 2 show examples in which the liquid inlet passage and the liquid outlet passage are separately formed in the syringe or adapter, but the liquid outlet passage may be connected to a middle part of the liquid inlet passage. Figs. 3 and 4 show filter prewetting apparatuses according to such an embodiment. Namely, the filter prewetting apparatuses according to the embodiments shown in Figs . 3 and 4 relate to the filter prewetting apparatus defined above, characterized in that a liquid outlet passage 50, 51 is branched from a middle part of a liquid inlet passage 52, 53. It is obvious for those skilled in the art that this structure can also be used to easily prewet a filter in a manner similar to that employed by the apparatus shown in Fig. 1. The components of the filter prewetting apparatus, such as the piston, the cylinder, the attachment and the adapter, can be made from any moldable material. Each component of the filter prewetting apparatus, can be molded from a suitable material chosen from, for example, fluororesins such as polytetrafluoroethylene (PTFE) ; other polymer resins such as polypropylene, polyvinyl chloride, polyethylene; glass or metals such as stainless steel, considering the resistance to various liquids, strength, durability, weight or moldability, etc. The check valve can be made from fluororesins, chemical resistant rubbers, metals or other materials .

According to another aspect of the invention, an apparatus for wetting a filter 80 comprises a pump 81 which has a suction port 82 and a pressure port 83, as shown in Fig. 8. The suction port 82 is adapted to be directly or indirectly connectable to a port 84 of a filter 85 to draw a liquid 86 through the filter 85 into the suction port 82 of the pump 81. The liquid may be discharged from the pump 81 through the pressure port 83. Preferably the filter 85 is immersed in a liquid 86 contained in a vessel 87 during the prewetting operation. The pump 81 may also be immersed in the liquid 86, or it may be installed outside the vessel 87. Preferably the liquid discharged from the pump 81 is returned to the vessel 87 although it may be discharged to any other place.

Similar to the apparatus shown in Fig. 1, the apparatus 80 may also include an attachment 90. The attachment 90 is substantially similar to the attachment 22 shown in Fig. 1. A main difference between attachments 22, 90 is that while the attachment 22 is attachable to the liquid inlet 15 of the syringe 11, the attachment 90 is attachable to the suction port 82 of the pump 81. Similar to the end of the syringe 11 shown in Figs. 9a and 9b, the suction port 82 or the end of the attachment 90 which is adapted to be connectable to the filter may be configured to be connectable to more than one type of filter. The pump 81 may be a pump of any type and capacity, as long as it generates sufficient vacuum at its suction port 82 to draw a liquid through the filter 85. For example, the pump 81 may be a gear, vane, piston, diaphragm, bellow or magnet pump, and it may have a fixed displacement or variable displacement. The pump 81 may also be a manual pump, or it may be powered by a prime mover 88 such as an electric, pneumatic or hydraulic motor.

According to another aspect of the invention, the apparatus 80 may also include an automatic control device which may sense whether the filter 85 is sufficiently wetted and, if so, automatically stop the liquid flow through the filter 85. The automatic control device may be configured in a number of ways. For example, in the embodiment shown in Fig. 8, the automatic control device includes a controller 91 and a sensor. The controller 91, which may be coupled to any of the components of the wetting apparatus including both the prime mover 88 and the sensor, may be any suitable electronic controller such as a microprocessor or a logic array. The sensor monitors the wetness of the filter 85 .

The wetness of the filter 85 can be determined in a number of ways. For example, the pressure difference across the filter 85 and the speed of the prime mover 81 may be used to determine the wetness of the filter 85. This is so because the pressure difference across a given type of filter is a function of the wetness of the filter and the flow rate through the filter, and for a given pump displacement, the flow rate can be estimated approximately from the speed of the prime mover. When the filter 85 is not sufficiently wetted, a higher pressure difference across the filter 85 is required to draw liquid through the filter 85 for a given speed of the prime mover 88 (or flow rate through the filter) because the filter has higher resistance to liquid flow. When the filter 85 is sufficiently wetted, on the other hand, a lower pressure difference across the filter 85 is required to draw liquid through the filter 85 for the same speed of the prime mover 88. The pressure difference at which the filter 85 is sufficiently wetted can be determined experimentally for a given speed of the prime mover 88. Alternatively, the pressure inside the filter, i.e., the pressure at the suction port, can be used to determine the wetness of the filter 85 if the pressure outside the filter is the atmosphere pressure, as shown in Fig. 8. Higher pressure difference across the filter 85 means lower pressure inside the filter 85 (higher degree of vacuum) if the pressure outside of the filter 85 is equal to the constant atmosphere pressure. The liquid flow through the filter 85 can be stopped in a variety of ways. For example, a variable displacement pump such as a vane or piston pump may be employed, and the liquid flow through the filter 85 can be stopped by setting the displacement, thus the flow rate, of the pump to zero. The pressure difference across the filter 85 may be used to control the displacement of the variable displacement pump and set it to zero when the filter 85 is sufficiently wetted. Alternatively, a controller 91 may be employed to receive a signal from a sensor such as the pressure sensor 89 sensing the pressure difference across the filter 85. When the pressure difference reaches or falls below a predetermined value indicating the filter 85 is fully wetted, the controller 91 may shut off the prime mover or set the displacement of the pump to zero to stop the liquid flow through the filter 85. A further alternative is that the time it takes to wet a filter can be determined empirically, and the pump 81 can be shut off after the predetermined amount of time. A still further alternative is to provide a valve arrangement between the filter and the pump and to stop the liquid flow through the filter by closing the valve arrangement or by allowing liquid flow to the pump to bypass the filter. The valve arrangement can be controlled manually or automatically by a controller.

Although different variations of the filter prewetting apparatus embodying this aspect of the invention are described above, it is sufficient to use only the one shown in Fig. 1 to illustrate how they may be employed to prewet filters because others can be used in substantially the same manner.

Advantages of the invention As evident from the foregoing description, the filter wetting or flushing apparatus and the methods according to this invention can be used to easily and rapidly wet or flush a filter at the location where the filter is being used. In addition, the filter wetting or flushing apparatus according to this invention has the following advantages:

1. Because the filter is placed in the suction line of the pump or the syringe, the liquid does not damage the filter medium of the capsule-type filter during wetting or flushing operation because the liquid flows from the primary side to the secondary side of the filter but does not flow backward.

2. A filter wetting or flushing apparatus or method with automatic control is more efficient both in time and in cost, and does not require monitoring by an operator.

3. Due to its readily portable lightweight and compact nature, many embodiments of the filter wetting or flushing apparatus can be readily carried into, for example, a clean room of a semiconductor manufacture line. There is no limitation on the place where it is used and a great benefit lies in it cost effectiveness because no power supply or pressure pump or other equipment is needed for many of the embodiments. Further, in the absence of this equipment, the sources of dust are minimized and the problem of contamination in a clean room is avoided. 4. For many of the embodiments, only a small space is occupied and a small amount of liquid suffices because only a liquid vessel completely receiving a filter and a liquid in an amount to fill the vessel are needed. The liquid is not wasted because it is recycled through a liquid outlet tube in the liquid vessel.

5. The prewetting method can take place rapidly, even in an emergency, as compared with the immersion method.

6. The problem of contamination of liquid is reduced because the flow of liquid is shorter and simpler than in the pressurization method.

7. Maintenance is easier because fewer components are needed.

8. During the prewetting treatment of a filter, the bubbles adsorbed on the secondary side of the filter are readily removed and do not remain in the filter because the liquid is drawn into the suction port while the opening of the filter is oriented upward.

9. Any type of filter can be wetted or flushed using the same pump or syringe by changing the attachment. A capsule-type filter in which a filter cartridge is received in a housing can also be directly prewetted or flushed by coupling the suction port of the pump to one opening in the filter housing and coupling the liquid to the other opening in the filter housing. 10. For the embodiments which use an adapter, a commercially available syringe can be used. Therefore, a syringe of an optimal size can be used in accordance with the size of the filter to be treated.

As evident from the foregoing description, the filter wetting or flushing apparatus and methods according to this invention offers great industrial value because they can be used to wet or flush a filter easily, efficiently and economically.

Example

A filter prewetting apparatus according to this invention having the structure shown in Fig. 3 was made from tetrafluoroethylene resin by cutting. The thus prepared apparatus had the following sizes: 50 mm in outer diameter of the syringe, 300 mm in length of the syringe, 34 mm in inner diameter of the cylinder, 140 ml in discharge volume of the cylinder, 10 mm in diameter of the liquid channel of the attachment. This apparatus was used to prewet a cylindrical cartridge-type filter: ENFLON AB1FD3EJ made by Pall Corporation. The filter was formed of a filter material made from polytetrafluoroethylene pleated into a cylinder having a rated filtration mesh of 0.05 mm, an outer diameter of 71 mm, an inner diameter of 40 mm and a length of 313 mm. The attachment was fitted to the syringe of the filter prewetting apparatus according to this invention by means of an O-ring and the filter was fitted to the attachment by means of an O-ring. A 3000-ml vessel is filled with a liquid isopropanol (EL grade) , in which the filter was completely immersed so that the forward end of the liquid outlet tube of the filter prewetting apparatus may be located in the liquid. The filter was prewetted by three cycles of reciprocation of the piston.

The thus prewetted filter was placed in an apparatus for determining flow rate-pressure loss characteristics shown in Fig. 5 and water was circulated at appropriately varying flow rates to measure pressure losses. A cleanup filter of 0.05 mm was provided upstream of the test filter to remove particulate materials in the circulating water. During the measurement, the filter was protected from the secondary side pressure. Then, the filter was removed and the apparatus was operated to measure the piping pressure loss, which was subsequently subtracted from the previous measurements to determine pressure losses of the filter. The pressure loss values were expressed as those values in water at 20°C by correction for viscosity. The results are shown in Table 1 and Fig. 6.

Comparative Examples 1 and 2

A 3000 ml vessel was filled with isopropanol, in which the same filter as used in the above Example was immersed with its opening upward and retained in the liquid for 30 minutes to prewet the filter. Pressure losses of thus prewetted filter were determined by the same procedure as described in Example (Comparative Example 1) . Pressure losses of the same filter, which was laterally thrown in the same vessel and immediately removed, were also determined in the same manner (Comparative Example 2) . The results are shown in Table 1 and Fig. 6.

The results shown in Table 1 and Fig. 6 demonstrate that the filter prewetted by the filter prewetting apparatus according to this invention shows better (lower) pressure loss values after the operation of only three cycles (in only ten and a few minutes as expressed by time) than the filter treated by the throwing method and also shows a better result than the filter immersed for 30 minutes, confirming that the apparatus of this invention ensured a sufficient prewetting treatment.

Claims

1. An apparatus for wetting or flushing a filter comprising: a syringe composed of a cylinder and a piston and having formed therein a liquid inlet communicating with the barrel space of the cylinder through a liquid inlet passage and a liquid outlet communicating with the barrel space through a liquid outlet passage; and an attachment, one end of which is constructed to be removably engaged with said liquid inlet of said syringe, another end of which is constructed t be removably engaged with the opening of the filter to be wetted or flushed, which has a liquid passage communicating with said both ends formed therein; characterized in that a check valve allowing liquid flow from said liquid inlet to said barrel space of said cylinder but checking reverse liquid flow is provided in said liquid inlet passage in said syringe, and a check valve allowing the liquid fl Low from said barrel space of said cylinder to said liquid outlet but checking reverse liquid flow is provided in said liquid outlet passage in said syringe .

2. An apparatus for wetting or flushing a filter comprising: an adapter having a syringe connection port, a liquid inlet and liquid outlet, and having formed therein a liquid inlet passage communicating between said syringe connection port and said liquid inlet and a liquid outlet passage communicating between said syringe connection port and said liquid outlet; and an attachment, one end of which is so constructed that it is removably engaged with said liquid inlet of said adapter, another end of which is so constructed that it is removably engaged with the opening of the filter to be wetted or flushed, which has a liquid passage communicating said both ends formed therein; characterized in that a check valve allowing liquid flow from said liquid inlet to said syringe connection port but checking reverse liquid flow is provided in said liquid inlet passage in said adapter, and a check valve allowing liquid flow from said syringe connection port to said liquid outlet but checking reverse liquid flow is provided in said liquid outlet passage in said adapter .

3. The apparatus for wetting or flushing a filter according to claim 1 or 2 wherein one end of said liquid outlet passage is connected to the intermediate portion of said liquid inlet passage so that said liquid outlet passage is branched from said liquid inlet passage and communicates with said liquid outlet.

4. An adapter for use in an apparatus for wetting or flushing a filter which has a syringe connection port, a liquid inlet and liquid outlet, and has formed therein a liquid inlet passage communicating between said syringe connection port and said liquid inlet and a liquid outlet passage communicating between said syringe connection port and said liquid outlet; characterized in that a check valve allowing liquid flow from said liquid inlet to said syringe connection port but checking reverse liquid flow is provided in said liquid inlet passage, and a check valve allowing liquid flow from said syringe connection port to said liquid outlet but checking reverse liquid flow is provided in said liquid outlet passage, and said liquid inlet is so constructed that an attachment for connecting the filter to be wetted or flushed is removably engaged with said liquid inlet.

5. An apparatus for wetting or flushing a filter comprising a syringe including a cylinder and a piston disposed in the cylinder; a liquid inlet and a liquid outlet, each in fluid communication with a barrel space of the cylinder, said liquid inlet being adapted to be connectable to a port of a filter to draw a liquid through the filter into the liquid inlet to wet or flush the filter; and a valve assembly coupled to the liquid inlet and the liquid outlet, said valve assembly allowing liquid flow from the liquid inlet to the barrel space of the cylinder but blocking reverse liquid flow, and allowing the liquid flow from the barrel space of the cylinder to the liquid outlet but blocking reverse liquid flow.

6. The apparatus for wetting or flushing a filter according to claim 5 wherein the syringe is a dual action syringe that includes a cylinder and a piston disposed in the cylinder, and the piston divides a barrel space of the cylinder into first and second chambers, each chamber in fluid communication with the liquid inlet and the liquid outlet, and wherein the valve assembly which is coupled to the inlet and the outlet allows liquid flow from the liquid inlet to the first and second chambers but blocks reverse liquid flow, and allows liquid flow from the first and second chambers to the liquid outlet but blocks reverse liquid flow.

7. The apparatus for wetting or flushing a filter according to claim 5 or 6 further comprising an attachment having first and second ends and a flow path providing fluid communication between the first and second ends, said first end being connected to the liquid inlet and said second end being attachable to the port of the filter, whereby the liquid inlet is adapted to be indirectly connectable to the port of the filter through the attachment.

8. The apparatus for wetting or flushing a filter according to claim 5 or 6 wherein the valve assembly comprises a spool valve.

9. The apparatus for wetting or flushing a filter according to claim 5 wherein the valve assembly comprises first and second check valves, the first check valve being disposed between the barrel space of the cylinder and the liquid inlet and allowing liquid flow from the liquid inlet to the barrel space of the cylinder but blocking reverse liquid flow, and the second check valve being disposed between the barrel space of the cylinder and the liquid outlet and allowing the liquid flow from the barrel space of the cylinder to the liquid outlet but blocking reverse liquid flow.

10. The apparatus for wetting or flushing a filter according to claim 6 wherein the valve assembly comprises first, second, third and fourth check valves, the first check valve being disposed between the first chamber and the liquid inlet and allowing liquid flow from the liquid inlet to the first chamber but blocking reverse liquid flow, the second check valve being disposed between the first chamber and the liquid outlet and allowing the liquid flow from the first chamber to the liquid outlet but blocking reverse liquid flow, the third check valve being disposed between the second chamber and the liquid inlet and allowing liquid flow from the liquid inlet to the second chamber but blocking reverse liquid flow, and the fourth check valve being disposed between the second chamber and the liquid outlet and allowing the liquid flow from the second chamber to the liquid outlet but blocking reverse liquid flow.

11. An apparatus for wetting or flushing a filter comprising a pump including a suction port and a pressure port, said suction port being adapted to be connectable to a port of a filter to draw a liquid through the filter into the suction port.

12. The apparatus for wetting or flushing a filter according to claim 11 further comprising an attachment coupled to the suction port of the pump and having first and second ends and a flow path between the first and second ends, said first end being connected to the suction port, whereby the suction port is adapted to be indirectly connectable to the port of the filter through the attachment.

13. An apparatus for wetting a filter comprising, a pump coupled to the filter and providing a liquid flow through the filter; a prime mover coupled to the pump to power the pump; and an automatic control device operatively associated with the prime mover, said automatic control device including a sensor, said sensor sensing directly or indirectly the wetness of the filter, wherein the automatic control device stops the liquid flow through the filter when the filter is sufficiently wetted.

14. An apparatus for wetting or flushing a filter comprising, a pump coupled to the filter and providing a liquid flow through the filter; a prime mover coupled to the pump to power the pump; and an automatic control device operatively associated with the prime mover, said automatic control device including a pressure sensor, wherein the pressure sensor senses the pressure difference across the filter and the automatic control device stops the liquid flow through the filter when the pressure difference reaches predetermined values.

15. The apparatus for wetting or flushing a filter according to claim 14 wherein the automatic control device sensing the speed of the prime mover, whereby the automatic control device stops the liquid flow through the filter when the pressure difference across the filter reaches predetermined values for a given speed of the prime mover.

16. A method for wetting or flushing a filter comprising drawing a liquid through the filter into a suction port of a pump.

17. The method for wetting or flushing a filter according to claim 16 further comprising attaching a port of the filter to the suction port of the pump and immersing the filter in a liquid.

18. The method for wetting or flushing a filter according to claim 17 wherein attaching a port of the filter to the suction port of the pump includes attaching a port of the filter to an attachment having first and second ends and a flow path providing fluid communication between the first and second ends, and attaching the first end of the attachment to the suction port of the pump.