US3295359A

US3295359A - Air sampler

Info

Publication number: US3295359A
Application number: US324936A
Authority: US
Inventors: Robert D Peck
Original assignee: Controlled Environment Equipment Corp
Current assignee: Controlled Environment Equipment Corp
Priority date: 1963-11-20
Filing date: 1963-11-20
Publication date: 1967-01-03
Anticipated expiration: 1984-01-03

Description

3 Sheets-Sheet 1 ROBERT D. PECK ATTORNEYS R. D. PECK AIR SAMPLER v v? F INVENTOR 2a FFI FIGZ Jan. 3, 1967 R. D. PECK 3,295,359

AIR SAMPLER Filed Nov. 20, 1965 5 Sheets-Sheet 2 INVENTOR ROBERT D. PECK BY 3%, %J2W, fi/komfwam ATTORNEYS Jan. 3, 1967 R. D. PECK 3,295,359

AIR SAMPLER Filed Nov. 20, 1965 5 Sheets-Sheet 5 INVENTOR. ROBERT D. PECK ATETORNEYS United States Patent 3,295,359 AIR SAMPLER Robert D. Peck, Needharn, Mass, assignor to Controlled Environment Equipment Corporation, Whitman, Mass., a corporation of New York Filed Nov. 20, 1963, Ser. No. 324,936 8 Claims. (Cl. 7328) The present invention relates to an air sampler for sampling the amount of contamination in an atmosphere, especially in a clean room.

An object of the present invention is to provide such an air sampler which is self-contained, compact, light in weight, portable, simple and foolproof in design, and simple and inexpensive to manufacture but rugged in construction, which accurately and reliably collects on a filter, the dirt in a measured volume of air drawn through the sampler, in which such filter is conveniently located at a readily accessible location at the air inlet to the sampler and can be easily mounted in position on the sampler, removed and replaced without the necessity of tools, and without opening the sampler. Preferably, the filter is removably secured in a filter holding unit which can be slipped on and off the sampler and is a membrane filter.

Yet another object is to provide such a portable, selfcontained sampler in which the operating parts thereof which create contamination, such as the pump and motor, are enclosed in a sealed casing so that the contamination created thereby cannot escape to. the external atmosphere, whereby the entire sampler unit can be placed and operated in a clean room without adding contamination to the room. The filter in the air inlet is located outside the easing so that the filter can be easily changed without opening the casing.

Yet another object is to provide an easily accessible and changeable filter in the gas exhaust from the sampler which removes any contamination introduced into the air during passage through the various working parts of the sampler so that no contamination greater in size than the exhaust filter limitation can remove to the external atmosphere, whereby the entire sampler unit can be placed and operated in a clean room with the exhaust air discharged into the room without adding contamination to the room. Preferably, the exhaust filter is a membrane filter.

Yet another object is to provide an improved self-contained, portable air sampler to sample the amount of contamination in an enclosure by placing the entire air sampler in the enclosure and turning it on, whereupon a measured volume of air in the enclosure is automatically passed through the sampler including a filter at the air inlet, which removes contamination, followed by removing the filter and quantitatively measuring the contamination deposited on the filter.

Yet another object is to provide a portable, self-contained air sampler for sampling contamination in an adjustable and regulated measured volume of an atmosphere with no contamination being added by the sampling device to the atmosphere being sampled.

Yet another object is to provide such a sampler which embodies (1) a time switch for automatically turning off the pump (which moves the air through the sampler) a predetermined time after it is turned on, and (2) an adjustable valve and air flow gauge for regulating the rate of flow, to provide a simple and effective means for regulating the size (volume) of an air sample and insure the same size sample each time.

Other objects and advantages will become apparent from the following description and the accompanying drawings of an embodiment of the air sampler of the present invention, in which drawings:

FIG. 1 is a view in perspective of the air sampler embodiment;

Patented Jan. 3, 1967 FIG. 2 is a view in elevation of the air sampler of FIG. 1 with the rear casing wall removed and partially in section and with the dust cap of the inlet filter unit removed;

FIG. 3 is an exploded view in section and in perspective of the inlet filter unit of FIG. 1;

FIG. 4 is an exploded view in section and in perspective of the exhaust filter unit of FIG. 1;

FIG. 5 is a View taken through section 55 of FIG. 2.

FIG. 6 is a view in vertical section through the air inlet portion of the sampler of FIG. 1 showing the air inlet filter and its holder and the manner in which such holder is mounted on the sampler.

Referring to the drawings, 2 represents an air sampler embodying the present invention comprising a sealed, rectangular casing 4 comprising a floor 6, having four feet 7, and a cover 8 having a top wall 8a and four depending side walls (front and

rear walls

8b and 8c, respectively, and two end walls 8a) which depend around the periphery of floor 6, as shown, and which have an internal ledge 9 for screwing the cover 3 to the floor 6 of the casing, as shown, with a sealing gasket 9a between the floor 6 and ledge 9. The top wall has a carrying handle 10.

Located within the sealed casing 4 is a vacuum pump 12 operated by an electric motor 14, also located in the casing. The motor and pump assembly are mounted on the floor 6 of the casing by means of a bracket 7a mounted on four rubber washers 11, the bracket and washers being secured to floor 6 by four nylon bolts 13.

Pump 12 suck air or other gas in from the atmosphere outside the casing through (1) the inlet filter unit 16 mounted outside the casing, (2) an elongated, rigid inlet orifice tube 18 extending through the casing end wall in an air tight manner and on which inlet filter unit 16 is mounted, (3) a flexible hose 20 inside the casing, (4) a conventional combined needle valve and air flow gage 19 mounted on the front casing wall 8b outside the casing and comprising a needle valve 21 operable by knob 23 outside the casing and an air flow gage 22 also located outside the casing, (5) flexible hose 24 inside the casing to (6) the pump inlet 26 and thence through (7) the pump 12, (8) the pump outlet 28, (9) a conventional type muf fler 34) mounted on the motor outlet and also located in side the casing, (10) a flexible hose 32 located inside the casing, (11) a rigid, elongated outlet orifice tube 34 extending through the casing end Wall in an air tight manner and finally (12) the outlet filter unit 36 located outside the casing and mounted on outlet orifice 34.

Also located inside the sealed casing is a conventional type time switch 33 located in motor circuit 39 for turning on the motor and shutting it off a predetermined adjustable time after it has been turned on, and a thermal switch 40 which is mounted on and is a part of the motor and is located in the motor circuit 39 to turn off the motor in the event of over-heating thereof. The timer switch 38 is mounted on the front casing wall.

The motor circuit wiring 39 extends into a cord 42 which passes through the casing floor in an air tight manner and terminates in a plug 42a. The motor circuit wiring is provided with connectors 42!).

Timer switch 33 is provided with a control knob 41 and a dial 43 located outside the casing, which knob, when turned to the desired time on the dial 43, closes the timer.

switch to start the motor. The timer switch is automatically opened to shut off the motor after the motor.

has operated for the set time. The control shaft of the timer switch on which knob 41 is mounted, extends through the front wall of the casing in an air tight manner.

The combined valve and gage unit 1-is conventional and comprises a transparent, elongated, plastic block 45 provided with metal fittings 46 and 4-8 molded in the plastic block at its ends, which metal fittings have shanks 46a and 48a, respectively, which extend horizontally out of the rear face of the block through the front casing wall in an air tight manner. Hoses 24 and 20 are attached to shanks 46a and 48a respectively. Plastic block 45 has a calibrated vertical passage i).

Fittings

46 and 48 each have a passage which extends horizontally from the shank end inside the casing and then vertically to communicate with the ends of vertical passage 50 located in the plastic block 45. The horizontal passage in lower fitting 48 hasv a needle valve 21 therein operated by knob 23. A ball 47 of calibrated weight is located in passage 50 directly over the outlet of the vertical passage in lower fitting 48 and is lifted by the upward flow of air from such vertical passage, the amount of lift depending on the rate of flow. In this way, the rate of flow can be measured and regulated by observing and regulating the height of the ball by means of the needle valve and the calibrations on the gage. The fit of the ball in passage 50 is loose enough to permit the flow of air thereby.

The inlet orifice member 13 comprises an elongated metallic member 52 of circular cross section and externally threaded and having an orifice bore 54 (e.g. /32 inch diameter) extending therethrough, a flange 56 and a tapered outer end portion 58, such elongated member extending through and fast in an end wall of the casing with flange 56 abutting the outer surface of the wall. Orifice member 18 is held fast in the casing wall in an air tight manner by means of a nut 54a and sealing washer 5412, such nut being threaded tight over the threaded portion of member 52 to pull the flange 56 tightly against the outer surface of the casing wall. A sealing ring (not shown) may be provided between flange 56 and the outside surface of the end wall.

The inlet filter unit 16 comprises a transparent plastic filter holder made up of (1) a cup-shaped supporting member 60 having a disc-shaped base 61 with a central hole 63 adapted to be forced tightly onto the tapered end 58 of the inlet orifice member 18, (2) a transparent plastic cup-shaped screen 62 the annular side wall 64 of which is swedged within the annular side wall 66 of member 60 with a tight friction fit and the disc-shaped base 68 of which is perforated to form a screen, (3) a disc-shaped membrane filter '70 held flush and snugly against the screen 68 by means of (4) a transparent, plastic retaining ring 72 also fitting within the end portion of member 60 with a tight fit and having an outwardly turned flange 74, and (5) a transparent plastic removable cap 76 the open end of which fits snugly but removabiy within the retaining ring 72, as shown. Cap 76 protects the filter until the sampler is to be used, at which time the cap is removed. After the sample has been taken, the cap is again moved into place. The inside diameters of the side wall 64 of the screen 62 and of retaining ring 72 are the same.

The inlet filter unit 16 can be mounted, removed and replaced simply by pushing the unit 16 onto and pulling it off the tapered end 58 of the inlet orifice member.

The outlet orifice member 34 comprises an elongated nylon member 80 of circular cross-section and having an orifice bore 82 (e.g. inch diameter) therethrough and an integral disc-shaped flange 84 at one end through which the bore extends. The periphery of member 80 is threaded. Member 86 extends through the casing end wall, as shown, and is held fast in the wall by nut 83 and sealing washer 83a, the nut 83 being threaded over member 80 to pull flange 84 tightly against the outside surface of the casing wall. A sealing ring may be provided between flange 84 and the casing wall. The periphery of flange 84 is threaded. A disc-shaped membrane filter 86 (e.g. 1.850 inch diameter) is held over the outer flat surface of flange 84 and a disc-shaped wire screen 88 (e.g. 50 mesh) of the same diameter as the filter is held pressed against the filter by means of a retaining ring 90 threaded over the threaded flange 84, and O-ring .4 being located and squeezed between the filter and flange 84 to provide a seal by screwing the ring tight.

The sampler is operated in the following manner.

With the power cord 42 connected to an electrical power source and the membrane filter holder unit 16 in place on the inlet orifice member 18 but with the cap 76 removed, the knob 41 of time switch 38 is rotated clockwise to the desired operating period in minutes and released, thus starting the motor and activating the vacuum pump 12. The vacuum pump 12 draws air from the surrounding atmosphere through the filter 79, which has a specific known surface area, screen 68 and orifice 54, thence through hose 20 to and through the needle valve 21 and air-flow gage 22, and through hose 24 into the vacuum pump 12. Air is exhausted from the vacuum pump through mufller 30 (integral with the vacuum pump), hose 32, exhaust orifice 82, membrane filter 86 and screen 88. Thus, all air from the exhaust pump exits to the surrounding atmosphere through filter 86. The timing switch turns off the vacuum pump automatically after the time for which the switch has been set has elapsed. The volume of air per unit time drawn through the sampler and hence through the inlet filter 7 0 is determined by setting the needle valve and air-flow gage to restrict flow to a desired flow rate (in standard cubic feet per hour), the most desirable setting being 50 standard cubic feet per hour. A sample of air is the total volume drawn through the filter 7t and is determined by the settings of the air-flow gage which restricts volume per unit time and the time switch 38 which restricts total time of flow.

As aforesaid, the entire operating mechanism is assembled in sealed box 4 which rests on feet 7 and is carried by the handle 10.

Since all the operating parts are sealed in the casing, contamination produced by the operation thereof cannot contaminate the atmosphere and since the exhaust gas is filtered, none of the contaminants entrapped in the air by passage through the unit can contaminate the atmosphere. Consequently, the entire portable unit can be placed anywhere in the clean room or other enclosure to take samples without adding contaminants. This is extremely important since it is essential in clean rooms that the amount of dirt particles and other contaminants be kept at a minimum, the air in such room being carefully processed to remove contaminants. In fact, the reason why an air sampler is required is because contamination in the clean room must be kept below a certain maximum.

In the past, it has been necessary to kee the pump and other operating parts out of the room and to exhaust the air from the sampler out of the room. This necessitated either fixed sample removing stations or the use of tubing extensions to draw the air out of the room through the sampling unit, both of which have disadvantages which are avoided by means of the simple, portable unit of the present invention. The portable sampler of the invention need only be carried anywhere into the room and the timer turned on to take a sample, after which the inlet filter unit can be easily removed and replaced by another. When sampling is completed, the sampler is simply carried out of the room.

After a sample has been taken and the inlet filter unit removed, the inlet filter can be easily removed from the filter unit without disturbing the dirt and other contaminants deposited on the filter by removing retaining ring 72. Thereafter, the number of dirt particles deposited are counted under a microscope. This technique is described in the ASTM Method No. F 25-63T entitled, Sizing and Counting Airborne Particulate Contamination in Clean Rooms and Other Dust-Controlled Areas Designed for Electronic and Similar Applications.

Knowing the total volume of air passed through the sampler (rate of flow indicated on gage multiplied by time of flow indicated on timer dial) and the amount of contaminants removed from such volume, i.e. the amount of contaminants contained in such volume and deposited on the inlet filter, concentration of contaminants per unit volume of air in the clean room is known.

One type of membrane filter which can be used in the air inlet and exit is one sold by the Millipore Filter Corporation under the name Millipore Filter and described in its bulletin, Detection And Analysis of Contamination, published November 1962. However, other types can also be used.

The embodiment of the invention described and shown is for illustrative purposes only and the invention is not intended to be limited thereto or thereby, such invention being limited only to those constructions which are covered by the following claims and their equivalents.

I claim:

1. A portable :air sampler for sampling the amount of contaminants in the atmosphere in an enclosure comprising a sealed casing, a pump, a motor for said pump, and a timer switch in the circuit of said motor, said pump and motor being enclosed within said sealed casing, a How control valve operable from outside said casing to control rate of flow, said timer switch being operable from outside the casing, an air conduit comprising an air inlet and an air outlet extending through said casing and conduit means providing communication between said air inlet, said control valve, said vacuum pump and said air outlet, the inlet of said air conduit located outside of said casing having a replaceable filter therein to collect contaminants in the sample of atmosphere drawn through said sampler by said pump, the outlet of said air conduit located outside of said casing having a replaceable filter therein to remove any additional contaminants picked up by said atmosphere during passage thereof through the sampler and thereby prevent contamination of said atmosphere in said enclosure by said last mentioned contaminants, said sealed casing preventing the escape of contaminants from said motor and pump to said atmosphere in said enclosure.

2. An air sampler according to claim 1, said timer switch being located within said sealed casing.

3. An air sampler according to claim 2, a gage associated with said valve and located outside of said casing for quantitatively indicating the rate of flow through said sampler, said timer switch automatically turning off motor operation an adjustable, visually indicated time after actuation, whereby the total air sample passed through the sampler may be readily computed by multiplying the indicated rate of flow and the indicated time of flow.

4. An air sampler according to claim 3, said motor having a muflier at its outlet, said muffler also being located in said sealed casing.

5. An air sampler according to claim 1, said air outlet comprising an elongated outlet orifice member extending through the casing wall in an air-tight manner and having a restricted bore therethrough and a flange at its outer end outside the casing, said outlet filter being removably mounted on the outer face of said flange over said bore.

6. An air sampler according to claim 5, including a screen located over said outlet filter and a removable 6 retaining ring to retain said screen and filter in position on said flange.

7. A portable air sampler for sampling the amount of contaminants in the atmosphere in an enclosure comprising a sealed casing, a pump, a motor for said pump, and a timer switch in the circuit of said motor, said pump and motor being enclosed Within said sealed casing, a flow control valve operable from outside said casing to control rate of flow, said timer switch being operable from outside the casing, an air conduit comprising an air inlet and an air outlet extending through said casing and conduit means providing communication between said air inlet, said control valve, said vacuum pump and said air outlet, the inlet of said air conduit located outside of said casing having a replaceable filter therein to collect contaminants in the sample of atmosphere drawn through said sampler by said pump, the outlet of said air conduit located outside of said casing having a replaceable filter therein to remove any contaminants picked up by said atmosphere during passage thereof through the sampler and thereby prevent contamination of said atmosphere in said enclosure by said last mentioned contaminants, said sealed casing preventing the escape of contaminants from said motor and pump to said atmosphere in said enclosure, said air inlet comprising an elongated inlet orifice member extending through the casing wall in an air-tight manner and having a restricted bore therethrough, the end portion of said orifice member protruding outside said casing being tapered, said filter being part of a filter unit adapted to be placed on and pulled olT said tapered portion to mount and remove the filter unit in operative position on and from the casing.

8. An air sampler according to claim 5, said inlet filter unit comprising a cup-shaped support, the base of which is provided with a hole for clamping over said tapered portion of said orifice member, said cup-shaped support containing a screen comprising a cup-shaped member, the base of which is provided with perforations and the side of which is snugly received within the side of said support, said cup-shaped screen being inverted with respect to said support, said filter being held against the outside surface of said screen by a retaining ring 'removably secured to said support, a cap removably secured to said support and located over said filter.

References Cited by the Examiner UNITED STATES PATENTS 1,517,144 11/1924 Anderson 7328 2,065,970 12/1936 Hartzell 55-473 2,135,036 11/1938 Karlstrom 55-473 X 2,484,202 10/ 1949 Wintermute 73-28 2,819,774 1/1958 Schmidt et a1 55-270 X 3,109,724 11/1963 Heckman et a1 73--28 X 3,232,094 2/1966 Teschner 73-28 RICHARD C. QUEISSER, Primary Examiner. J. FISHER, Assistant Examiner.

Claims

1. A PORTABLE AIR SAMPLER FOR SAMPLING THE AMOUNT OF CONTAMINANTS IN THE ATMOSPHERE IN AN ENCLOSURE COMPRISING A SEALED CASING, A PUMP, A MOTOR FOR SAID PUMP, AND A TIMER SWITCH IN THE CIRCUIT OF SAID MOTOR, SAID PUMP AND MOTOR BEING ENCLOSED WITHIN SAID SEALED CASING, A FLOW CONTROL VALVE OPERABLE FROM OUTSIDE SAID CASING TO CONTROL RATE OF FLOW, SAID TIMER SWITCH BEING OPERABLE FROM OUTSIDE THE CASING, AN AIR CONDUIT COMPRISING AN AIR INLET AND AN AIR OUTLET EXTENDING THROUGH SAID CASING AND CONDUIT MEANS PROVIDING COMMUNICATION BETWEEN SAID AIR INLET, SAID CONTROL VALVE, SAID VACUUM PUMP AND SAID AIR OUTLET, THE INLET OF SAID AIR CONDUIT LOCATED OUTSIDE OF SAID CASING HAVING A REPLACEABLE FILTER THEREIN TO COLLECT CONTAMINANTS IN THE SAMPLE OF ATMOSPHERE DRAWN THROUGH SAID SAMPLER BY SAID PUMP, THE OUTLET OF SAID AIR CONDUIT LOCATED OUTSIDE OF SAID CASING HAVING A REPLACEABLE FILTER THEREIN TO REMOVE ANY ADDITIONAL CONTAMINANTS PICKED UP BY SAID ATMOSPHERE DURING PASSAGE THEREOF THROUGH THE SAMPLER AND THEREBY PREVENT CONTAMINATION OF SAID ATMOSPHERE IN SAID ENCLOSURE BY SAID LAST MENTIONED CONTAMINANTS, SAID SEALED CASING PREVENTING THE ESCAPE OF CONTAMINANTS FROM SAID MOTOR AND PUMP TO SAID ATMOSPHERE IN SAID ENCLOSURE.