GB2067268A

GB2067268A - Suction regulator device for a compressor

Info

Publication number: GB2067268A
Application number: GB8034942A
Authority: GB
Original assignee: ISARTALER SCHRAUBENKOMPRESSOREN GmbH
Current assignee: ISARTALER SCHRAUBENKOMPRESSOREN GmbH
Priority date: 1979-10-31
Filing date: 1980-10-30
Publication date: 1981-07-22
Also published as: FR2468771A1; SE8007643L; BE885954A; JPS5718482A; DE2944053C2; FR2468771B1; JPH0116344B2; IT8025702A0; GB2067268B; IT1133731B; SE450652B; DE2944053A1

Abstract

A suction regulator device for opening and closing the suction duct 4 of a compressor comprises a closure member 9 movably mounted about a cylinder 5 push fitted into a boss 1 formed on a wall 2 of the inlet duct of the compressor. To member 9 is fixed a control piston 6 which is acted upon by spring 15 to urge annular seal 10 into sealing engagement with surface 11. On starting up, operating pressure via duct 24, bore 21 and radial passage 23 acts on pressure face 20 of the piston 6 to move member 9 to the left. Supply system pressure is applied, in opposition, to pressure face 29 via line 16 and regulator valve 17, magnetic valve 18 and/or pneumatic valve 19. <IMAGE>

Description

SPECIFICATION Suction regulator device for a compressor The invention relates to a suction regulator device for a compressor, particularly but not exclusively for a screw compressor with oil injection, including a member which opens and closes the suction duct under the action of a spring and is connected to a control piston which is guided in a cylinder.

Such a device is known from the German Gebrauchsmuster 7,811,860, in which the closure member is urged in the opening direction by means of a compression spring. By means of the control piston, the suction duct can be closed, against the spring force, when, on reaching the switching-off pressure, compressed air is applied to the piston from, for example, a pneumatic tripout regulator. In the case particularly of a screw compressor with oil injection, a suction regulator device of this type can undertake only limited control functions.

The object underlying the invention is to provide a suction regulator device, of the kind described in such a way that it can carry out several control functions in a reliable manner, whilst being of simple construction.

According to the invention there is provided in or for a compressor a suction regulator device including a movable member adapted to open and close the suction duct, said member being urged by a spring in the duct closing direction and movable by a control piston under the action of pressure generated by the compressor in the duct opening direction.

The spring force can be overcome, and the suction duct opened, by the pressure generated as the compressor starts up. To shut the suction duct, a control pressure, for example the supply system pressure, can be applied to the control piston in the direction of the spring force, so that the operating pressure acting an the opposite end of the piston is overcome. A special check valve can thus be omitted, such a valve normally being provided in the case of a screw compressor with oil injection in order to prevent oil from the oil reservoir escaping, through the compressor, into the suction duct when the compressor is switched off, due to the fact that the operating pressure still prevails in the oil reservoir on switching-off.

A proportional control system, in which the movement of the movable member is infinitely variable as a function of the compressed air demand, can be obtained by making it possible to apply the pressure present on the consumer side (supply system pressure) to the control piston in the duct closing direction.

In order to obtain, on the one hand, a delay in the opening of the suction duct when the compressor is switched on and, on the other hand, to achieve sensitive movement of the movable member during proportional control, the pressure area of the piston, to which area the operating pressure of the compressor is applied, may be designed in such a manner, in relation to the spring force, that the spring force can already be overcome at a very low operating pressure.

A delay in the opening of the suction duct on switching the compressor on is facilitated by forming a bore, having a small cross-section, in the cylinder on the supply system pressure side of the control piston, this bore communicating with the suction side of the compressor.

In a preferred embodiment an electric and/or a pneumatic regulator device is located in the line carrying the supply system pressure to the control piston, so that the suction regulator device can be electrically and/or pneumatically controlled by applying a control pressure to the supply system pressure side of the control piston.

For venting air from the oil reservoir, in the case of a screw compressor with oil injection, the movable member can be provided with a bore which, when the element is in the closed position, can be connected to the operating pressure side of the control piston, or to the line carrying the operating pressure: In order that the invention may be readily understood, an embodiment thereof will now be described by way of example with reference to the accompanying drawing, which is a sectional view of a regulator.

The suction regulator device, which is of cylindrical form overall, is set into a boss 1 on a housing wall 2 of the compressor Opposite this housing wall 2, a further housing wall 3 is located, in which a suction duct 4 is secured, coaxial to the suction regulator device and to the boss 1. This suction duct 4 can be surrounded by an air-filter cartridge, which is not illustrated. The space between the housing walls 2 and 3 communicates directly with the suction opening of the compressor.

A cylinder body 5 is secured in the boss 1, by being pressed-in, for example. A control piston 6 is slidingly located in the cylinder body 5, the shaft 7 of the piston extending through the end wall 8 of the cylinder body and carrying a closure member 9 at its free end. This closure member 9, which has the shape of a truncated cone at its leading portion, is provided with a sealing ring 10, on an annular surface located normal to the longitudinal axis, this ring engaging in a leak-tight manner on the seating surface 11 of the suction duct 4 when the closure member 9 is in the closed position.

The closure member 9, which is of approximately pot-shaped design overall, includes a skirt portion 12 in the form of a cylindrical shell, the longitudinal dimension of which is somewhat larger than the length of the stroke of the closure member 9. The closure member 9 is guided, bv means of skirt portion 12 on a bushing sleeve 5 on the external periphery of the cylinder body 5, a seal being located in an annular groove 13 at the end of the skirt portion and sliding on the peripheral surface of the cylinder body 5. A ventilation opening 14 is formed in the closure member 9 which provides a connection between the suction duct 4 and the cavity which exists between the closure member 9 and the cylinder body 5 when the former is in the closed position.

Opening 14 equalises the pressure on both sides of member 9 and largely eliminates forces which would otherwise occur on the closure member 9, during its stroke movement, as a result of different pressures on the two sides of the closure member.

The control piston 6 is subjected in the direction of closing to the action of a compression spring 15 which is supported against the housing wall 2 and is located in a recess in the control piston 6. In addition, the control piston 6 can be subjected to the pressure of the supply system, which is supplied by the compressor, via a line 16, which is led through the housing wall 2, coaxially with the longitudinal axis of the compression spring 1 5. The pressure in the line 1 6 is taken off, on the compressor, downstream of the check valve located in the pressure line, or downstream of the pressure-holding valve. A proportional regulator, known per se, is shown schematically at 17.

As indicated by broken lines, a magnetic valve 18 and/or a pneumatic valve 19 may also be connected to the line 16, whereby a control pressure can be applied to the control piston 6, by means of a pneumatic or electric control system, in order to close the suction duct 4.

The pressure, generated directly by the compressor, is applied, in the direction of opening, to the control piston 6, on an annular piston area 20. A bore 21 passes through the cylinder body 5 parallel to the piston axis, this bore opening into an annular groove 22, from which a radial bore 23 opens into the cylinder space. The annular groove 22 is covered, in a leak-tight manner, by the bushing 5', whose outer surface forms the guide surface for the closure member 9. The longitudinal bore 21 communicates with a line 24, which is led through the housing wall 2 and is connected to the pressure side of the compressor or, for example, to the oil reservoir, and thus leads the pressure directly generated by the compressor to the control piston 6.

The cylinder body 5, which is approximately potshaped, has shoulder 25 at the open end, on which shoulder is disposed a sealing ring separating, in a leak-tight manner, the cylinder space which is pressurized by the line 16, from the pressure line 21,24.

An axial bore 26, having a radial section, passes through the control piston 6 and its shaft 7. When the closure member 9 is in the closed position, the bore 26 communicates with a radial bore 27, formed in the cylinder body 5, so that the pressure side of the compressor is in communication with the atmosphere, via these bores 26, 27, and the oil reservoir is vented when the compressor is switched off or when the suction regulator device is closed.

The strength of the compression spring 15 is designed in such a manner, in relation to the pressure are 20 on the control piston 6, that a low operating pressure of the compressor is already sufficient to displace the control piston 6 against the force of the compression spring 15. The compression spring 15 is preferably designed such that the spring force corresponds approximately to a pressure of one bar on the pressure area 20 of the control piston.

In addition, a bore 28, having a small crosssection, is formed in the housing wall 2, this bore connecting the cylinder space, which is pressurized by the line 1 6, to the suction side of the compressor. This bore 28 can emerge, for example, in the space between the housing walls 2 and 3.

The pressure area 29 on the control piston, which is pressurized by the line 16, can, for example, be designed so that it is twice as large as the opposite pressure area 20. Depending on the strength of the compression spring 15, another ratio of the pressure areas 20,29 can also be provided. The pressure area 29, which acts together with the spring 1 5 in the direction of closing, is advantageously larger than the pressure area 20.

The compression spring 1 5 is advantageously designed such that it just holds the control piston in the closed position when the suction of the suction side is present at the pressure area 29. If the pressure on the pressure area 20 is low, the control piston is then pushed into the open position.

The suction regulator device can be controlled from three different points (proportional regulator 17, electric valve 18 and pneumatic valve 19), thus allowing proportional control and open-shut control from the electric side or from the pneumatic side.

The suction regulator device functions as follows. When the compressor is switched off, the closure member 9 holds the suction duct 4 shut, under the force of the spring 1 5. The line 16 is connected to the atmosphere, via one of the valves 18, 19. The pressure side of the compressor, or the oil reservoir, is also connected to the atmosphere, via the line 24 and the bores 21,27,26.

If the compressor is switched on, a certain pressure is built up which acts on the pressure area 20 of the control piston, whilst at the same time a certain suction is built up, via the bore 28 which communicates with the suction side, so that, after the compressor starts up, the control piston 6 is displaced somewhat towards the left.

At the same time, the connection between the bores 26 and 27 is interrupted and the venting of the pressure side is thus terminated. The control piston 6 can be driven into the completely open position, as illustrated, at an operating pressure of approximately 1 bar.

In regulated operation, with infinitely variable setting of the suction regulator device, the line 16 is connected to the supply system, via the proportional regulator 1 7. Since the pressure area 29 on the control piston 6 is larger than the pressure surface 20, which is subjected to the operating pressure, the suction regulator device remains open as long as a pressure smaller than the operating pressure minus the spring force prevails downstream of the proportional regulator 17. When this pressure downstream of the proportional regulator 17 approaches the operating pressure minus the spring force, the control piston begins to move to the right. In the illustrative embodiment described, the suction regulator device begins to close the suction duct 4, when for a final pressure of 7 bar, the supply system pressure reaches 6 bar.In regulated operation, the suction regulator device opens automatically, in a corresponding manner, when the supply system pressure falls again.

In another mode of operation of the compressor,the line 16 can be connected to the atmosphere, via one of the valves 18, 19, so that the suction regulator device is in the fully open position, as illustrated, during the operation of the compressor. In dependence on an electrical or pneumatic control system, a control pressure for the immediate closing of the suction duct 4 can be imparted to the pressure area 29, via one of the valves 18,19. The supply system pressure is advantageously employed as a control pressure. In the case of such continuous operation, the suction duct 4 is merely opened and closed, without the closure member 9 taking up intermediate positions as in the case of regulated operation.

An isolating valve in the line 1 6 is marked 30.

Various modifications of the construction designed are possible. Thus, the vent bore 26 in the control piston can be omitted, or an exchangeable restrictor can be inserted into the leading part of the closure member 9.

Claims

1. In or for a compressor a suction regulator device including a movable member adapted to open and close the suction duct, said member being urged by a spring in the duct closing direction and movable by a control piston under the action of pressure generated by the compressor in the duct opening direction.

2. A device according to claim 1 including means for applying the supply system pressure to the control piston to urge it in the duct closing direction.

3. A device according to claim 2 in which a bore of small cross-section is formed in the piston cylinder on the supply system pressure side of the control piston, this bore communicating with the suction side of the compressor.

4. A device according to claim 2 or 3 in which the pressure area of the control piston, to which area the supply system pressure can be applied, is larger than the pressure area to which the operating pressure is applied.

5. A device according to any of claims 2 to 4 in which an electric and/or a pneumatic regulator device is provided in a line carrying the supply system pressure to the control piston for the purpose of applying a control pressure to the control piston.

6. A device according to any of the preceding claims in which the pressure area of the control piston acted upon by the operating pressure of the compressor, is such that only a very low operating pressure is required to overcome the spring force.

7. A device according to any of the preceding claims in which the movable member is provided with a bore which in the closed position can be connected to the operating pressure side of the control piston, or to a line carrying the operating pressure.

8. A device according to any of the preceding claims in which the movable member is of a potshaped design and is guided on a cylinder body by means of a portion in the form of a cylindrical shell, a pressure-equalizing bore being provided in the member.

9. In or for a compressor a suction regulator device substantially as hereinbefore described with reference to the accompanying drawing.