NO20180426A1 - Double-acting pump device based on reciprocating piston - Google Patents

Description

The invention relates to a double-acting device which is designed to utilize the energy in a supplied driving fluid to produce a defined pressure increase in a supplied pump fluid, and which is based on a reciprocating piston arrangement.

The pump device is designed to be able to operate with high pressure levels, and preferably includes a stabilization unit that is designed to maintain a stable flow and pressure level both on the drive side and on the pump side, and thereby minimizes mechanical stress on the pump unit and on equipment that is operated of this pump device is arranged so that the driving medium is returned from the pump device to a reservoir which is virtually pressureless or which has approximately the same pressure as the surrounding medium.

- The pump device comprises a housing with a drive section and a pump section. Pressure energy from the drive fluid is transferred from the drive section to the pump section via a drive piston which is part of a piston arrangement, and which has a roughly dimensioned piston rod which is led leak-free through a partition between the drive section and the pump section. The drive piston separates the drive section into two drive chambers, which due to the roughly dimensioned piston rod has significantly different cross-sections.

The drive chamber with the smallest cross-section is permanently pressurized by having an open connection with the drive medium inlet. It is thereby possible to force the piston arrangement to reciprocate and transfer energy to the fluid in the pump section by means of a switching mechanism which causes switching between a first operating state where the drive chamber with the largest cross-section is in open connection with the inlet and shut off from the outlet, and a second operating state where the drive chamber is shut off from the inlet and in open connection with the outlet. This switching is controlled in cooperation between the aforementioned switching mechanism and a control rod which has a mechanical connection to the drive piston.

Norwegian patent 340558 relates to a pump device which is designed to pump liquid from virtually pressureless tanks which are installed in the sea. This pump device has several features that are common to the invention in question, and is considered to represent the closest known technique. This technique cannot be configured to create a desired depth-independent relationship between the drive pressure (= overpressure of the drive medium in relation to the ambient pressure) and the pressure increase that is achieved on the supplied pumping medium. This means that this technique is not suitable for solving the following three types of tasks which the invention in question is particularly designed to handle;

1. As a pressure-boosting pump - i.e. using a drive fluid's overpressure in relation to ambient pressure to produce a desired pressure increase in a pump fluid that initially has approximately ambient pressure.

2. As an intensifier - i.e. utilizing a drive fluid's excess pressure in relation to ambient pressure to raise the pressure in a part of this drive fluid, or possibly to increase the pressure in a pump fluid that has the same pressure as supplied drive fluid.

3. As a low-pressure pump – i.e. using a drive fluid's excess pressure in relation to ambient pressure to remove liquid from tanks that are virtually depressurised. The liquid is preferably discharged to a reservoir which is pressure equalized with the surroundings or directly to the surroundings.

The starting point for the operation of a pump device according to the invention has been that for a given configuration the relation (PH-PREF)/(PS-PREF) must have the same constant value (K1) regardless of the sea depth. Correspondingly, a given configuration of a pump device that is to take care of task type 3 must have a constant value for the relation K2 = PAMB/(PS-PAMB). This relationship reflects that the pump device necessarily requires an increase in the drive pressure at increased depth, as the pressure in the pump medium must be raised from approximately zero to ambient water pressure.

As will be apparent from appendix 1, all dimensional parameters in a pump device according to the invention can be determined unambiguously based on a selected value for K1 or K2. The calculations do not take into account friction in sealing rings etc., but qualitatively speaking this has little practical significance. The real value of K1 will be somewhat lower than the calculations indicate, while K2 will be somewhat higher.

In a pump device according to the invention, the piston arrangement is designed so that a third chamber appears in the pump section, and by matching the relative size of the piston arrangement's contact surfaces to the pump device's five chambers, a desired balance can be achieved between the forces affecting the temple arrangement. The scope of application of the invention is not limited to the aforementioned areas of use. For example, this technology will be very well suited to producing a high hydraulic pressure with instrument air as the driving medium.

The invention will be described in more detail with reference to Figures 1 - 5 therein;

- Fig. 1 shows an outline of a pump system according to the invention, configured to be able to produce a desired pressure increase on a pump medium which is supplied with a pressure corresponding to the pump device's ambient pressure.

- Fig 2 A and B show two diagrams which indicate the pressure development at the outlet of the pump medium, with and without the use of a stabilization unit according to the invention. - Fig 3. shows a diagram of a stabilization unit which cooperates with a pump device as shown in fig. 1

- Fig 4 shows a drawing of a pump device according to according to the invention, configured to be used as an intensifier.

- Fig. 5A and Fig. 5B show two drawings of a pumping device according to the invention, configured to be able to pump liquid out of an almost pressureless tank

Definitions;

In the description, the term "chamber cross-section" is used. The chamber's cross-section A is defined as A= F/P, where F is the resultant of axially acting forces against the piston arrangement when the relevant chamber has pressure P.

Fig. 1 shows a pump device which is designed for task type 1, which means that both the drive medium's return pressure and the pump medium's supply pressure are approximately equal to the ambient pressure. This design is suitable for creating hydraulic pressure for operating a BOP or for chemical injection in an underwater well.

The pump device comprises a housing 23) with a drive section and a pump section which cooperate via the piston arrangement 1-3). This piston arrangement is composed of a drive piston 1) with a roughly dimensioned piston rod 2) and a first element 3) which is slidably arranged on a fixed second element 4). The piston rod 2) is led leak-free through a sliding seal 13) which is arranged in a partition wall 12) between the drive section and the pump section.

The drive piston 1) forms a displaceable barrier between two chambers IV,V) in the drive section. The thickness of the piston rod 2) means that the drive piston 1) has a significantly larger area directed towards chamber V than towards chamber IV. The drive piston 1) can thereby be reciprocated by placing chamber IV in a permanently open connection to the propellant supply line 24) via the inlet 22), and chamber V being alternately pressurized and vented by connecting to or drive medium inlet 21) and to the drive medium return line 18). The alternating pressurization and venting is provided by a switching mechanism built into the drive section's end wall 20). The switching mechanism comprises a switching valve, not shown, and an initiation valve, not shown, which cooperates with the piston arrangement 1-3) via the operating rod 16). When the drive piston approaches an end position, contact is achieved between an outgrowth 15) on the maneuvering rod and one of the two contact points 14,17) on the piston arrangement. After achieving contact, the operating rod is drawn into the piston arrangement's further displacement. This activates the initiation valve which initiates the exchange by pressurizing or vent a chamber in the switching valve.

A switching mechanism with this mode of operation is described in Norwegian patent 340558 and Norwegian patent application 2016 1801, and is therefore considered prior art.

The displaceable first element 3) in the piston arrangement is designed so that in cooperation with two sliding seals 8,10) it forms three chambers in the pump section;

- a first chamber I which is connected to the pump medium inlet 6) via a first directional valve 5), and which causes chamber I to be supplied with pump medium when it expands.

- a second chamber II which is compressed and expanded in counterphase with chamber I, and which via a second directional valve 7) is supplied with pump medium from chamber I when this is compressed.

- a third chamber III which, depending on which task the pump device is to perform, has an open connection with the drive medium's return line 18) or an open connection with the pump medium's inlet 6).

The pump function works as follows;

- When the piston arrangement is shifted to the right, chamber I is compressed, and the liquid which this chamber took up during the last expansion is pressed into chamber II via the second directional valve 7). In a preferred embodiment, the first element 3) is designed so that chamber I has twice the cross-section of chamber II. This means that only half of the pump medium that is pushed out of chamber I can be absorbed by chamber II. The remaining half is pushed out of the outlet of the pump medium 9). In the embodiment shown, a directional valve is not arranged on the outlet 9). Chamber II will therefore have the same pressure as the consumer connected to the outlet 9).

- When the drive piston is moved to the left, chamber II is compressed, and the pump medium that fills this chamber is pushed out of the outlet 9). At the same time, chamber I expands and draws in new pump medium from the inlet 6) via the first directional valve 5).

Because chamber I has twice the cross-section of chamber II, it is achieved that equal amounts of pump medium are pumped out in both stroke directions.

If both the pump medium and the drive medium are a liquid, by dimensioning the pump device in accordance with the calculations in appendix 1, the following relationship will be achieved;

K1 = (PH-PREF)/(PS-PREF) = A5/A1

There ; PH= The absolute pressure of the pumping medium that is delivered,

PS= The absolute pressure of the supplied propellant

PREF= The absolute pressure at the outlets 11,19) = the pressure at the pump medium inlet 6).

A1 = cross section of chamber I,

A5 = cross section of chamber V.

The pump device which is outlined in fig. 1 is dimensioned so that A5/A1 = 3.5.

If, for example, PS is 100 bar above PREF, then the pump's outlet pressure will consequently be; PH= 3.5*100 = 350 bar above PREF.

A pump device based on a reciprocating piston arrangement will have a drop in the fluid delivery as the piston arrangement changes stroke direction. Each switching operation entails large changes in speed both in the relevant fluids and in moving components with some considerable mass. This can generate pressure transients which in turn can lead to a significantly reduced lifetime for the pump device as well as for equipment that the pump device must serve. A pump device according to the invention comprises in a preferred embodiment a stabilization unit (26) which, by maintaining an unchanged level of the fluid flows while the piston arrangement changes stroke direction, counteracts deviations in the desired balance between drive pressure and pump pressure.

Figure 2A indicates how pressure and flow conditions vary at the outlet of the pump medium 9) if the pump device does not have such a stabilization unit. The pump device in question here has a pump frequency of 1 Hz. The dashed line indicates the level of delivery that is desired to be maintained.

Fig 2B indicates the corresponding pressure and flow sequence for a constellation with a pump device and a stabilization unit according to the invention.

Fig 3 shows an outline of such a constellation. The stabilization unit consists of a housing 33) with a piston 27) which defines three chambers in the housing 33);

- Chamber VI which is in open connection with the propellant supply line 24) via a channel 31).

- Chamber VII which is in open connection with the propellant return line 18) via a channel 24)

- chamber VIII which is in open connection with the pump medium outlet 9) via a channel 25).

The stabilization unit is designed to compensate for reduced delivery of pressurized pump medium while the pump arrangement changes stroke direction. Chamber VIII must therefore absorb liquid from the pump device in the time between each switching operation, and release liquid while the switching operation is in progress.

In order for chamber VIII to be able to absorb liquid in the time between each switching operation, the net upwardly directed force against the piston 27) must exceed the friction in the piston's two sliding seals 27,29). In a preferred embodiment, the stabilization unit is dimensioned so that the pressure forces affecting the piston 30) in the axial direction will be in approximate equilibrium if the pump device is in normal operation and the spring 28) has been removed. From the figure it can be seen that upward and downward forces directed towards the piston 30) are in balance if;

PH*AH+ PREF(AS-AH) = PS* ASor (PH-PREF)AH=(PS-PREF)ASwhere AH is the piston area in contact with chamber VIII and AS is the piston area in contact with chamber VI.

Based on a pump device with K1 =3.5, a desired equilibrium will be achieved by the piston 30) being dimensioned so that; AH/AS= 3.5. The spring 28) can preferably be without tension when the upper end surface of the piston 30) lies directly below the upper inner wall in chamber VI.

The operation will be explained based on a relevant dimensioning of a pump device according to the invention;

A pump device according to the invention will typically be able to carry out a complete switching operation in approximately 50 milliseconds. The pump frequency is set to 1 Hz.

Piston arrangement 1-3) has a stroke length of 100 mm, and the drive piston 1) has diameter A1=120 mm. This means that the piston arrangement in this embodiment will have a maximum speed of 20 cm/sec. During the 50 milliseconds required to carry out a switching operation, the piston should have moved approximately 10 mm. The real displacement during this operation will be approx. 6 mm, distributed over both strike directions. We use an amplification factor K1=3.5. This means that the pumping device will have a delivery deficit of pumping medium corresponding to a volume V= A1/3.5*4 mm = 13 cm3. This means that the stabilization unit must be able to supply 13 cm3 of liquid with each individual switching operation. We choose to dimension the piston 30) so that AH= 20 cm2, which gives chamber VIII an inner diameter of approx. 50 mm. Consequently, the piston 27) will be displaced by approx. 7 mm with each switching operation.

To achieve the desired power balance, it is required that AS= 3.5*AH= 70 cm2. It may be relevant to use a spring 28) with a spring constant of size k= 10 kp/mm. In that case, the spring tension will be reduced by 70 kp while the pump fluid is released from the stabilization unit, corresponding to the delivery pressure dropping by 3.5 bar. One must expect a certain amount of adhesion in the piston's 27) sealing rings, so that the pressure at the stabilization unit's outlet 25) drops 1 - 2 bar before this friction is overcome. The piston 30) can thereby easily come into minor oscillations. To counteract this, the channel 31) is relatively narrow, and a one-way valve 32) is arranged parallel to this. This one-way valve will allow a rapid supply of driving medium to chamber VI, so that the piston 27) gets a rapid downward displacement when it has to compensate for drops in the delivery of pumping medium. It becomes more time-consuming to push the piston upwards as the fluid must then be forced out of chamber VI via channel 31).

At each switching operation, the stabilization unit must compensate for the lack of delivery from the pump device by supplying an estimated 13 cm of pump fluid within 50 milliseconds. When chamber VII is refilled, you have about 450 milliseconds at your disposal. The channel 31) can thus be relatively narrow without capacity problems arising.

Fig. 4 shows an embodiment where a pump device according to the invention is configured to be used as an intensifier. This embodiment is essentially similar to the embodiment in fig. 1, but in order to achieve the desired relationship between the drive pressure (PS-PREF) and the pump medium's delivery pressure (PH-PREF), it is necessary to change the relative size of the internal chambers in the pump device. Appendix 1 shows calculations related to an intensifier design. The following connection is obtained;

K1 = (PH-PREF)/(PS-PREF) = (A5/A11)

There ; PH= The absolute pressure of the pumping medium that is delivered,

PS= The absolute pressure of the supplied propellant

PREF= The absolute pressure at the outlets 15,20)

A5= the cross section of Chamber V

A1= cross section of chamber I

In these calculations, it has been assumed that chamber I has twice the cross-section of chamber II, i.e. that A3= 2*A4, so that equal amounts of pump fluid are delivered in each of the stroke directions.

It appears from the appendix that the prerequisite for achieving the desired relationship between drive pressure and delivery pressure is that the piston arrangement is then dimensioned so that:

A1= A5/(K1-1), A4= A5*0.5 *(K1-2)/(K1-1)

With a chosen value for Kl, the mutual dimensioning of the pump device's components will be unambiguously determined. Fig. 4 shows a drawing of an intensifier which is dimensioned for the same Kl factor as the traditional amplifier pump shown in fig. 1, i.e. K1 = 3.5.

Fig. 5 A and 5 B show drawings of two pumping devices which are designed to be able to pump liquid out of an almost pressureless tank and out to the surrounding sea, or to a reservoir which is pressure equalized with the surrounding sea. The pump devices in fig. 5A and 5B are configured for K2 values of respectively 1 and 2.

The operation is described with reference to the embodiment in fig. 5A;

The first element 3) is designed as a sleeve, and is slidably arranged on an external guide on the permanently mounted second element 4).

The piston arrangement 1-3) defines three chambers in the pump section;

a first chamber I which has a cross-section A1 which is defined by the internal diameter of the chamber.

a second chamber II which has a cross-section A2, and which is delimited by the inner walls of the drive section, the outer surface of the first and the second element, as well as the surface of the part of the piston rod 2) which lies inside the drive section. Here A2= π*( , where R2 is the diameter of the piston rod 2) and R4 is the radius of the guide on the outer surface of the second element 4).

- a third chamber III which has a cross-section A3, and which is delimited by the volume that appears between the two sliding seals 8,10). Chamber III is in open connection with the inlet 6).

The pump function works as follows;

When the piston arrangement 1-3) is displaced to the left, the mechanism within the dashed frame 34) ensures that, via the operating rod 32), a leftward pull is exerted which pulls the valve body 5) out of its seat 36) in the second element 4), thereby allowing the pump fluid to flow into chamber I via the internal channel in the second element 4). The displacement also causes a compression of chamber II, so that the pump medium that fills this chamber is pushed out of the outlet 9). The outlet 9) can be connected to a reservoir not shown which is pressure equalized with the surroundings - or which is possibly open to the surroundings. The mechanism 34) causes the pull in the operating rod 32) to cease just before the piston arrangement has reached the end point, and a right-hand spring tension causes the valve 5) to be quickly pressed back against the seat 33).

When the piston arrangement is shifted to the right, chamber I is compressed, and the pumping medium that this chamber took up during the previous expansion is pushed out through the other direction s controlling valve 7). Chamber II is compressed and expanded in counterphase with chamber I, and as we choose to let the effective cross-section of chamber II be half the cross-section of chamber I, half of the extruded volume is taken up by chamber II. The remaining half is pushed out of the outlet 9). In this way, the same amount of pump medium will be delivered in both stroke directions.

In Norwegian patent 340558, a purely mechanical tilting mechanism is used to control the opening and closing function for a directional control valve which essentially has the same function as in the invention in question. This rocker mechanism causes an almost instantaneous change between the open and closed state when the piston arrangement approaches an end stop. We consider alternative solutions for controlling the first direction's control valve to be prior art.

In this embodiment, two oppositely directed surfaces on the first element 3) are affected by the pressure in chamber II.

From fig. 5 we see that; A5-A4= π*R2<2>, and A1= π*R4<2>+ A3

where R2 is the diameter of the piston rod 2), R4 is the radius of the outer guide of the second element 4) and A3 is the cross section of chamber III.

Of this;

The value for A2 is used in the calculations in Appendix 1.

These calculations show that K2 = PAMB /(PS-PAMB)<=>A5/A1K2 the value should be chosen based on how large a drive pressure is available, and at what sea depth the pumping device must be able to be used.

The drive medium can be a non-lubricating medium, which with today's technology can typically limit the available drive pressure to 170 bar. This means that with K2= 1, the pumping device will have a maximum operational depth of approximately 1,700 metres.

A selected value for K2 implies an unambiguously defined mutual dimensioning of the pump device's five chambers.

Fig. 5 A shows a diagram of an embodiment with K2 = 1. Fig. 5B shows a corresponding diagram with K2 = 2, which may be an appropriate value if the pump device is to be able to be used at a depth of 3,000 metres.

When a pump device according to the invention is configured as a low-pressure pump, the outlet pressure will normally be stable equal to the ambient pressure, and there is consequently no need for any stabilization of the pump medium's delivery pressure.

Claims (3)

Claim 1. A double-acting pump device comprising a piston arrangement (1-3) which is slidably arranged in a pump housing (23), which is separated into a drive section with inlet (21,22) and outlet (11,19) for a drive medium and a pump section with inlet (6) and outlet (9) for a pump medium, and where the drive section comprises a switching mechanism that utilizes the difference between the drive medium's supply pressure and outlet pressure to reciprocate the piston arrangement (1-3) so that axially acting forces are transferred to the pump medium, thereby achieving a desired pressure increase, characterized by - the piston arrangement comprises a drive piston (1) which is displaceable in a cylindrical guide in the drive section and which has a roughly dimensioned piston rod (2) which can slide leak-free in a partition (12) between the drive section and the pump section, so that the drive section is separated into two drive chambers ( IV,V) which have different cross-sections, and where the drive chamber (IV) with the smallest cross-section is permanently open to the drive medium inlet (22), - the switching mechanism comprises a switching valve and an initiation valve which interacts with the drive piston (1) via a control rod (16) which is subjected to an alternating pull and push every time the drive piston (1) approaches an end point, whereby the initiation valve alternates between pressurizing or venting a chamber in the switching valve and thereby bring about a change between a first operating state where the drive chamber (V) with the largest cross-section is in open connection with the inlet (21) and shut off from the outlet (19), and a second operating state where the drive chamber (V) is shut off from the inlet (21) and in open connection with the outlet (19) - the piston arrangement also comprises a displaceable first element (3) which is connected to the piston rod (2) on the inside of the pump section and which is displaceable in relation to a fixed second element (4), and which cooperates with two sliding seals (8,10) so that virtually leak-free barriers are formed that separate a first (I), a second (II) and a third chamber in the pump section, where - the first chamber (I)) is connected to the pump medium inlet (6) via at least one directional valve (5) which is closed when the first chamber is compressed and which opens for the supply of liquid from the inlet when the first chamber (I) is expanded - the second chamber (II) has a smaller cross-section than the first chamber and is compressed and expanded in counterphase with the first chamber (I), - the second chamber (II) is connected to the first chamber (I) via at least one directional valve (7) which opens when the first chamber (I) is compressed whereby a given amount of the liquid emitted from this chamber (I) is occupied the second chamber (II) and the remaining part of the liquid are released via the outlet (9) of the pump medium, and which closes when the first chamber (I) is expanded whereby the liquid in the second chamber (II) is released via the outlet (9) - the third chamber (III) is a pressure compensation chamber which has an open connection with the drive medium outlet (19) or with the pump medium inlet (6) depending on which function the pump device is configured to perform 2. A double-acting pump device according to claim 1, characterized in that it cooperates with a stabilization unit (33) which consists of a housing with a slidably arranged piston (30) which is affected in the axial direction by the tension from a spring (28) and which separates the housing into three chambers (VI,VII,VIII) of which a first chamber (VI) is in permanent open connection with the propellant supply line (24), a second chamber (VII) is in open connection with the propellant outlet (19) and a third chamber (VIII) is in open connection with the outlet (9) of the pump medium, as said piston and spring are dimensioned so that during operation equilibrium is produced between the forces affecting the piston (30) in the axial direction, and that this equilibrium can be maintained by the piston can be displaced so that fluid is absorbed or released from the chambers (VI, VII, VIII). 3. A double-acting pump device according to claim 1, characterized in that it is dimensioned so that the first chamber (I) in the pump section has twice the volume change as the second chamber (II) in the pump section when the piston arrangement (1-3) is displaced