The present patent application relates to a minimum pressure valve.

In compressor installations a minimum pressure valve is mounted on the outlet of a pressure vessel that is used as a liquid separator.

By injecting a coolant during the compression of gas in a compressor element that forms part of a compressor installation, the temperature increase of the compressed gas can be kept within certain limits. A way to keep the coolant circulating in the compressor installation is to make use of the pressure difference that prevails over the cooling system of the compressor installation.

In practice this means that the coolant is driven through the compressor element of the compressor installation and enters the pressure vessel together with the compressed gas. There the coolant and gas are separated from one another .

The coolant is collected at the bottom of the pressure vessel and, from this point onwards, it is generally guided successively through a thermostatic valve, a coolant cooler and a coolant filter, to be finally injected into the compressor element again. During its passage through the cooling system the pressure of the coolant will fall. To ensure that the pressure of the coolant at the injection point in the compressor element is sufficiently high, the pressure in the pressure vessel must be kept at a sufficiently high level. This is realised by means of a minimum pressure valve.

This minimum pressure valve ensures that the pressure in the pressure vessel, during the loaded situation of the compressor installation, never falls below a certain minimum value. This minimum is the setpoint of the minimum pressure valve.

Normally these minimum pressure valves have one fixed setpoint that limits the pressure range in which a compressor installation can operate. To determine the lower limit of the operating pressure range, the setpoint of the minimum pressure valve, account must be taken of a number of preconditions and phenomena that can occur as described below.

The setpoint of a minimum pressure valve is set such that that coolant injection is guaranteed under all conditions. This also means that during transitional phenomena the pressure at the injection point is always high enough to prevent temperature peaks.

One critical transition occurs when the compressor installation goes from a loaded operating condition, whereby no gas is removed, to a condition with a very low resistance. For example when purging a borehole or in the initial phase of filling a large volume. When this happens, the pressure in the pressure vessel falls very quickly and at the same time the thermal load increases substantially because gas is suddenly being compressed again.

These two elements mean that the temperature inside the compressor element rises quickly. If the setpoint of the minimum pressure valve is higher, the pressure at the injection point will be higher. This will ensure that the temperature peak is lower.

During operation of a compressor installation, gas and coolant are mixed intensively. After separation of gas and coolant in the pressure vessel, small gas bubbles nonetheless remain in the coolant. When the pressure in the compressor installation falls quickly this results in these gas bubbles expanding such that the coolant can foam in the pressure vessel. Excessive foaming can result in the foam reaching the coolant separator element, for example, that is mounted inside the pressure vessel, which can adversely affect the separation efficiency or can lead to a transfer of coolant to the applications of the users. By selecting the setpoint of the minimum pressure valve to be sufficiently high the risk of this transfer due to this phenomenon can be prevented.

In very cold conditions the temperature of the coolant in the coolant cooler can be very low. Due to the combined effect of the increased viscosity of the coolant (which can be oil for example) in the coolant cooler, the bypass of coolant across the thermostatic valve and a lower injection pressure of the coolant at the temperature in the compressor element, in some cases it is necessary to increase the injection pressure of the coolant. With the minimum pressure valve it is possible to keep the injection pressure of the coolant high enough.

Normally these minimum pressure valves have one fixed setpoint that must be able to deal with the most critical situation. As a result the pressure range within which a compressor installation can operate is limited. With a variable minimum pressure valve a lower setpoint can be chosen and this is increased when one or more of the earlier discussed adverse situations occur.

Chinese patent application No. 101.520.103 describes a minimum pressure valve with a setpoint that can be manually adjusted by raising or lowering the counter-pressure at the back of the minimum pressure valve. In this way the spring force is assisted to keep the valve closed. Ά disadvantage of such a type of minimum pressure valve is that such a manual adjustment is slow and not sufficient to prevent the aforementioned problems during the transitional conditions of the compressor installation.

The purpose of the present invention is to provide a solution to at least one or more of the aforementioned and/or other disadvantages. To this end the present invention concerns a minimum pressure valve with a housing with an inlet and an outlet that are connected together by means of a chamber and to a valve body that is movable in this chamber, and in a closed position closes the aforementioned inlet by means of a spring whose first end can exert a force on the valve body, whereby this force determines the setpoint for opening the minimum pressure valve when the pressure at the inlet is greater than the aforementioned setpoint, and whereby the minimum pressure valve is provided with automatic adjustment means for varying the setpoint of the aforementioned minimum pressure valve on the basis of the operating conditions of a system connected to the aforementioned inlet of the aforementioned minimum pressure valve and/or on the basis of the operating conditions of a system connected to the outlet and/or on the basis of one or more environmental parameters.

In a compressor installation a variable minimum pressure valve will change its setpoint according to the pressure and temperature for example.

The setpoint of the minimum pressure valve will be low when an operating condition at low pressure occurs for a sufficient length of time and the ambient temperature is sufficiently high, while the setpoint will be high for operating conditions at high pressure or when the ambient temperature falls below a certain value.

This has a number of advantages. Indeed, by making the setpoint variable the pressure range within which the compressor installation can operate becomes wider because the minimum operating pressure can be reduced while:

the temperature peak during certain transitions remains under control;

- the foaming of the coolant in the pressure vessel can be prevented;

- the air speeds through the filter element are not too high.

The advantage of a wider operating range is that:

the fuel efficiency is increased when the installation is operating at low pressures;

- when making boreholes in rock or earth a lower minimum pressure is favourable for:

- running in a new hammer drill;

- when starting a borehole a lower pressure is less harmful to the wall of the borehole.

The invention also concerns a compressor installation that comprises a compressor element connected to a pressure vessel, whereby this pressure vessel is connected to an inlet of a minimum pressure valve with a housing with an inlet and outlet that are connected together by means of a chamber and to a valve body that is movable in this chamber, and in a closed position closes the aforementioned inlet by means of a spring whose first end can exert a force on the valve body, whereby this force determines a setpoint for opening the minimum pressure valve when the pressure at the inlet is greater than the aforementioned setpoint, and whereby the minimum pressure valve is further provided with automatic adjustment means for varying the setpoint of the aforementioned minimum pressure valve on the basis of the operating conditions of the compressor installation connected to the aforementioned inlet and/or of the applications connected to the aforementioned outlet that are supplied by the compressor installation and/or on the basis of one or more environmental parameters .

The invention further concerns a method for adjusting the setpoint of a minimum pressure valve of an installation, whereby this method comprises the following steps:

- the determination of the necessary pressure in the installation connected to the inlet of the minimum pressure valve and/or the installation at the outlet and/or the determination of another operating condition of the installation and/or the determination of one or more environmental parameters;

- the adjustment of the setpoint of the aforementioned minimum pressure valve on the basis of the determined pressure and/or the operating condition and/or the determined environmental parameter.

With the intention of better showing the characteristics of the invention, a few embodiments of a minimum pressure valve according to the invention are described hereinafter, by way of an example without any limiting nature, with reference to the accompanying drawings, wherein:

Figure 1 schematically shows a perspective view of a minimum pressure valve according to the invention;

figure 2 schematically shows a cross-section according to line II-II in figure 1; figure 3 schematically shows a variant of figure 2;

figure 4 schematically shows another variant of the section designated in figure 2 by F4 ;

figure 5 schematically shows another variant of figure 2;

figure 6 schematically shows another variant of figure 2.

The minimum pressure valve 1 according to the invention schematically shown in figures 1 and 2 comprises a housing with an inlet 3 and an outlet 4 that are connected together by means of a chamber.

In the drawings the inlet 3 is positioned on the underside of the minimum pressure valve 1, while the outlet 4 is positioned below at one side.

In the aforementioned chamber, a movable valve body 5 is provided with a sealing element 6a, 6b.

In a first closed position this sealing element 6a, 6b is pressed against a seat 7, whereby this seat 7 is located around the aforementioned inlet 3, by means of a spring 8 whose first end 9 exerts a force on the valve body 5. In this way the valve body 5 with the sealing element 6a, 6b closes the inlet 3.

In this case, but not necessarily, this sealing element 6a, 6b comprises a first part 6a and a second part 6b, which are affixed together and fastened to a valve stem 10 using fastening means 11 such as for example a bolt, screw, adhesive or any other suitable fastening means.

It is clear that the sealing element 6a, 6b can also be made of one whole unit or of more than two parts that are assembled together. Moreover, it is also possible that the sealing element 6a, 6b and the valve stem 10 form one whole unit . The valve stem 10 of the valve body 5 is affixed so that it can move axially in a section, whereby this section is called the non-return valve housing 12.

In this case, the non-return valve housing 12 is provided with a collar 13 extending in the peripheral direction and on the outside, which forms an abutment for the bottom wall 14 of a spring guide 15.

The spring guide 15 comprises, in addition to the aforementioned bottom wall 14, a side wall 16 extending upwards in the peripheral direction in which the aforementioned spring 8 at least partially extends.

The minimum pressure valve 1 is further provided with a spring housing 17 with a piston housing 18 mounted therein. The spring housing 17 is a part of the housing 2.

The piston housing 18 is provided with a cavity 19 in which a piston 20 is located that can move in the aforementioned cavity 19. The piston 20 is provided with an end surface 21 that rests on the second top end 22 of the spring 8 and can exert a force on it, while the aforementioned first end 9 of the spring 8 rests on the bottom wall 14 of the spring guide 15 and thus can exert a force on the valve body 5.

The space 23 defined by the spring housing 17, the piston 20 and the spring guide 15, in other words the space 23 in which the spring 8 is mounted, is in this case connected to the surrounding environment of the minimum pressure valve 1 via a small pipe 24 or tube through the wall of the spring housing 17, such that in other words the aforementioned space 23 is typically at atmospheric pressure. The piston 20 comprises a disk-shaped section 25, preferably with a groove that extends in the peripheral direction in which sealing means are provided, such as an O-ring 26 for example, that touches the inside of the side wall of the piston housing 18.

The aforementioned piston housing 18 is preferably provided with stop means 27 that prevent the piston 20 being able to exit the cavity 19 in the piston housing 18. These stop means 27 are for example, but not necessarily, a circlip or any other suitable end-stop means affixed in the piston housing 18.

The piston housing 18 can move in the longitudinal direction X-X' in the spring housing 17. A disk 28 is provided in the spring housing 17 that forms a top abutment for the piston housing 18. The aforementioned disk 28 can be moved in the longitudinal direction X-X' in the spring housing 17. In this case this can be done manually. In this way the spring tension can be increased or decreased by moving the spring 28 upwards or downwards because the disk 28 can exert a force on the aforementioned second end 22 the spring 8.

Figure 2 also shows a screw 29 that extends through the side wall of the spring housing 17 and a groove 30 extending in the longitudinal direction X-X' that is provided in the outside wall of the piston housing 18 to prevent the piston housing 18 being able to rotate in the spring housing 17. In this way an opening 31 can be made through the side wall of the spring housing 17, which in the drawings is aligned with an opening 32 through the side wall of the piston housing 18, and which is connected to a control valve not shown in the drawings .

The aforementioned opening 32 through the side wall of the piston housing 18 comes out in a space 33 that is enclosed by the piston housing 18 and the piston 20. In other words this space 33 is located above the piston 20.

The operation of the minimum pressure valve shown in figures 1 and 2 is as follows.

According to the invention the inlet 3 of the minimum pressure valve is connected to the pressure vessel of the compressor installation. The spring 8 exerts a force on the sealing element 6a, 6b via the spring guide 19, the nonreturn valve housing 12 and the valve stem 10, so that a certain pressure is required in the pressure vessel to lift up the sealing element 6a, 6b from the seat.

By moving the aforementioned disk 28 the spring tension, and thus the setpoint of the minimum pressure valve 1, can be adjusted. In other words this disk 28 forms adjustable means for manually adjusting the low setpoint of the minimum pressure valve 1.

When the space 33 above the piston 20 on the top second end 22 of the spring 8 is placed under pressure, the piston 20 will move downwards over a certain distance. This distance is such that it corresponds to a certain desired increase of the setpoint. When the piston 20 is placed under pressure, a greater pressure is required in the pressure vessel to lift up the sealing element 6a, 6b from the seat 7. If the piston 20 makes the maximum movement, up to against the stop means 27, the high setpoint is reached.

In other words the piston housing 18 with the piston 20, which can exert a force on the other, top, second end 22 of the spring 8, whereby the aforementioned space 33 can be placed under pressure via the opening 32 in the piston housing 18, form automatic adjustment means to automatically adjust the setpoint of the minimum pressure valve 1 between a low and a high setpoint, whereby this automatic adjustment means can change the force that the first end 9 of the spring 8 exerts on the valve body 5, in this case by changing the spring tension by compressing the spring 8.

The way in which the setpoint of the minimum pressure valve 1 is controlled by allowing or not allowing pressure in the space 33 above the piston 22 can be done in different ways.

For example a 3/2-way valve can be used that can be controlled by a control module, which for example monitors the pressure in the pressure vessel and/or the ambient temperature .

The control module will for example adjust the setpoint of the minimum pressure valve 1 according to a method according to the invention by determining the desired pressure in the pressure vessel and/or the ambient temperature and adjusting the aforementioned setpoint on the basis of this/these value (s) . It is also possible for the control module to adjust the setpoint on the basis of the current pressure and/or the past pressure for the inlet 3 of the minimum pressure valve 1 connected to the compressor element of the compressor installation and on the basis of the ambient temperature.

In this way it is possible to go to the high setpoint of the minimum pressure valve 1 when the pressure in the pressure vessel exceeds a certain value and/or when the ambient temperature falls below a certain value. When the pressure in the pressure vessel falls below a certain value for a certain time, the setpoint can be reduced again, Another way to implement the automatic adjustment means consists of making use of a motor, which, directly or otherwise, can drive means that can change the pretension of the spring, for example by turning a disk 28 or a screw such that the second end 22 of the spring 8 is moved.

In the case of the embodiment of figure 2, the piston housing 18 and the piston 20 can be removed for example and have the disk 28 directly determine the spring force on the sealing element 6a, 6b and the disk 28 can be driven, directly or indirectly, by a motor that can be controlled by a control element. By letting the motor turn in the one direction, the spring force on the sealing element 6a, 6b can be increased because the disk 28 is turned further in the spring housing 17, and by turning the motor in the other direction, the spring force and consequently the setpoint can be reduced.

Figure 3 shows a variant of figure 2, as an example of a different embodiment of a minimum pressure valve 1 according to the invention. In particular, the automatic adjustment means that change the force that the first end 9 of the spring 8 exerts on the valve body 5 are constructed in a somewhat different way. It is clear that the automatic adjustment means can be implemented in different ways in order to be able to change the aforementioned force and is not limited to the embodiments shown in figures 2 and 3. The minimum pressure valve 1 in figure 3 essentially differs from the one of figure 2 by the piston housing 18 and the piston 20 at the location of the aforementioned space 33 having a smaller diameter B than the diameter C of the inlet at the location of the valve body 5 when it is in the closed position.

As a result, the piston 20 will only move downwards when the pressure above the piston 20 is sufficiently higher than the pressure acting on the valve body 5.

Furthermore in figure 3 two different diameters at the piston 20 can be distinguished between, respectively a first diameter A of the disk-shaped section 25 of the piston 20 and a second, smaller diameter B of a protruding section 34 that extends on the aforementioned disk-shaped 25 section. The piston housing 18 has corresponding inside diameters A and B.

The piston housing 18 is configured such that the spring 8 only extends in the lower section of the cavity 19, whereby this section has the first larger diameter A. In this embodiment the aligned openings 31, 32 in the walls of the spring housing 17 and the piston housing 18 are connected to a volume 35, which in turn is connected to the pressure vessel of the compressor installation via a nonreturn valve 36. This non-return valve 36 is bypassed by means of a constriction 37. This non-return valve 36 only enables a gas flow through in the direction from the pressure vessel to the volume 35, but not in the other direction .

The constriction 37 can be realised in different ways, such as for example by means of a capillary, which has a variable or otherwise flow opening or by means of a different type of flow restriction elements such as a foam, a mesh or similar. The volume 35 can also be constructed in different ways, such as for example in the form of a small vessel, a pot, a pipe or similar whose internal volume can be adjusted or otherwise, or in any other suitable form in order to obtain the desired result.

In the embodiment shown in figure 3, the setpoint cannot be freely chosen, but it will change continuously when the pressure in the compressor installation falls very quickly and a setpoint reduction will be realised slowly.

In this case too, the low setpoint is determined by the force or pretension of the spring 8 on the valve body 5. The pretension of the spring 8 and thus this low setpoint can be adjusted by means of the disk 28.

The pressure in the pressure vessel is also allowed into the volume 35 and the space 33 above the piston 20 on the top of the minimum pressure valve 1. As the diameter B of the protruding section 34 on the aforementioned disk-shaped section 25 of the piston 20 is smaller than the diameter of the sealing element 6a, 6b of the valve body, or better said is smaller than the diameter C of the inlet 3 at the location of this sealing element 6a, 6b, the force of the piston 20 will be insufficient to move downwards against the force of the spring 8. The minimum pressure valve 1 is now set to the low setpoint.

But as soon as the pressure in the pressure vessel falls relatively quickly, the non-return valve 36 between the pressure vessel and the small vessel will prevent the pressure in the small vessel 35 falling. The force of the piston 20 is now greater than that of the sealing element 6a, 6b and the piston 20 will move downwards and increase the setpoint of the minimum pressure valve 1.

The constriction 37 is placed in parallel to the non-return valve 36, for example in the form of a small opening that will allow a small gas flow from the volume 35 to the pressure vessel. In this way, the pressure on the piston 20 falls slowly and thus the force that the piston 20 exerts, and the setpoint of the minimum pressure valve 1 will fall in a controlled way to the low setpoint.

The advantage of this is that there is no need for external control of the setpoint, such that a completely autonomous system is obtained. But it can be chosen to make the constriction and the non-return valve closable such that the setpoint can be selected and a partial transition is obtained from the high to the low setpoint. Figure 4 shows an alternative embodiment of the valve body 5 with the sealing element 6a, 6b and the non-return valve housing 12. The whole of the valve body 5 with sealing element 6a, 6b and the non-return valve housing 12 is replaced by a cylindrical valve body 38 that can move in the longitudinal direction X-X' of the housing 2. In this case, but not necessarily for the invention, the spring guide 15 is integrated with this cylindrical valve body 38.

An abutment 39 is provided in the housing 2 of the minimum pressure valve 1 that prevents the cylindrical valve body 38 from being able to leave the housing 2. The cylindrical valve body 38 will not close the minimum pressure valve 1 by being pushed against this abutment 39, instead of this a seal 40 is affixed in the housing 2 in the form of an 0- ring 40. This O-ring 40 will take care of the closing of the minimum pressure valve 1.

The cylindrical valve body 38 is provided with a small groove 41 and one or more openings 42. When the pressure in the pressure vessel increases, the cylindrical valve body 38 will move upwards against the force of the spring 8. Only when the aforementioned opening 41 reaches the aforementioned O-ring 40 will the minimum pressure valve 1 be opened. By suitably selecting the dimensions and location of the cylindrical valve body 38, the groove 41, the opening 42 and the O-ring 40, the pressure in the pressure vessel will have to exceed a certain level before the opening 41 reaches the aforementioned O-ring 40.

It is clear that it is also possible for the O-ring to be affixed to the cylindrical valve body 38 and the opening 41 as a cutaway in the housing 2 of the minimum pressure valve 1.

Figure 5 shows an alternative embodiment of figure 2, whereby in this case the means for manually adjusting the setpoint of the minimum pressure valve 1 is implemented in another way than by using the disk 28.

For the rest this embodiment is analogous to the one of figure 2. In this case the disk 28 is absent and the piston housing 18 is not affixed in the spring housing 17, but is affixed to the spring housing 17 by using a screw connecting piece 43. To this end the spring housing 17 is worked open at the top so that the spring 8 can extend through the spring housing 17 up to against the piston 20. The spring housing 17 is also provided with a screw thread 44 that can engage with the screw connecting piece 43.

An advantage of this embodiment is that the opening 32 of the space above the piston 20 can be turned. In other words the orientation or the location of this opening 32 can be changed independently of the outlet 4. This means that when the valve is mounted on the installation with the X-X' axis in the horizontal plane, the opening 32 can always be oriented downwards independent of the orientation of the outlet 4 of the minimum pressure valve 1. In this way condensate, formed during the transition from the high to the low setpoint or when stopped, or oil residues, are automatically removed. This is made possible because the cylindrical piston housing 18, that is provided with an extra edge, is held by an edge at the cylindrical hole in the screw connecting piece 43 through which the piston housing 18 is inserted. Between the two aforementioned edges a ring is mounted that minimises the friction between the two edges .

By tightening the screw connecting piece 43 to a greater or lesser extent on the spring housing 17, the piston housing 18 is brought downwards to a greater or lesser extent in the direction of the spring housing 17. In this way the spring tension can be adjusted.

For the rest the operation is analogous to that of the minimum pressure valve shown in figure 2. Figure 6 shows another alternative embodiment of a minimum pressure valve according to the invention.

While in figures 2, 3 and 5 the automatic adjustment means can change the force that the first end 9 of the spring 8 exerts on the valve body 5, in figure 6 these automatic adjustment means can change the area of the valve body 5 on which pressure in the pressure valve can act.

To this end a bush 45 is provided in the inlet 3, whereby this bush 45 has a small inside diameter D.

The sealing element 6a, 6b is provided with two diameters whereby the first part 6a is made stepwise thicker and on one side has a diameter that corresponds to the small inside diameter D of the bush 45, while on the other side the diameter corresponds to the larger diameter C of the seat 7 in the housing 2.

The bush 45 can move in the longitudinal direction X-X' in the inlet 3, such that the size of the inlet 3 at the level of the valve body 5 can be changed.

As a result the area of the sealing element 6a, 6b on which the pressure of the pressure vessel will act becomes smaller or larger, so that the sealing element 6a, 6b experiences a smaller or larger force. This will ensure that the setpoint of the minimum pressure valve 1 can be changed . It is clear that in this case the automatic adjustment means can only define two different setpoints, as is also the case for the embodiment of figure 3.

The bush 45 is held in a first position by a compression spring 46 that pushes against one side 47 of the bush 45. In this first position, as shown in figure 6, the section 48 of the bush with the small inside diameter D will seal around the step with small diameter D of the first part 6a of the sealing element 6a, 6b, so that the pressure of the gas in the pressure vessel can only act on a small area of the sealing element 6a, 6b. In other words a higher pressure is required in the pressure vessel to open the minimum pressure valve 1.

In order to be able to automatically move the bush 45, use is made of a pressure connecting port 49 that is affixed in the housing 2 and opens out on the other side 50 of the bush 45.

By means of a valve that is not shown in the drawing, the pressure connecting port 49 is connected to the pressure vessel. As a result the bush 45 can be pushed downwards against the force of the compression spring 46 towards a second position. As a result a compression chamber 51 occurs on the aforementioned other side 50 of the bush 45.

It is hereby important that the characteristics of the compression spring 46 and the working surfaces of the bush 45 are selected correctly. In the aforementioned second position of the bush 45, a larger inside diameter C of the bush 45 will be at the location of the seat 7 and the sealing element 6a, 6b. In other words, in this position the pressure of the gas in the pressure vessel can act on the large surface of the sealing element 6a, 6b, such that a lower pressure is required in the pressure vessel to be able to open the minimum pressure valve 1.

By means of the valve, the pressure connecting port 49 can be connected to the atmosphere, such that the pressure in the pressure chamber 51 will fall to atmospheric pressure and the bush 45 will be pushed back to the first position by the compression spring 46. A small channel 52 is provided in the housing 2 that connects the aforementioned pressure chamber 51 to the inlet 3 when the bush 45 is in the second position.

When the bush 45 returns to the first position, a space will occur formed by the bush 45, the valve body 5 and the housing 2. The air in this space can escape to the pressure chamber 51 via the small channel 52 and to the outside environment via the pressure connecting port 49. It is important that this small channel 52 forms a sufficiently large restriction so that the pressure in the pressure chamber 50 is sufficiently low while the aforementioned space is emptied. A seal 53, such as an O-ring for example, is also provided in the bush 45 so that no air can escape via the small channel 52 when the bush 45 is in the first position.

Although in all the examples shown above the spring 8 is constructed as a physical spring 8, it is possible to construct this spring 8 in different ways, such as for example in the form of a chamber that is brought to a specific pressure. The pressure in the chamber will as it were form the ^Λ spring force' or in other words exert a force on the valve body 5. By increasing or decreasing the pressure in the chamber the spring force' can be changed.

The present invention is by no means limited to the embodiments described as an example and shown in the drawings, but a minimum pressure valve according to the invention can be realised in all kinds of variants without departing from the scope of the invention