GB1597718A - Lubrication systems for air compressors - Google Patents

Description

(54) IMPROVEMENTS RELATING TO LUBRICATION SYSTEMS FOR AIR COMPRESSORS (71) We, COMPAIR CONSTRUCTION AND MINING LIMITED, a Company registered under the laws of England, of Camborne, Cornwall TR14 8DS, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to oil-flooded air compressors of the kind having an oil system for supplying a flow of lubricating and cooling oil under pressure to the compressor, which system is pressurised from a source of pressure which remains effective after the compressor has stopped running.

In an oil-flooded air compressor the oil system is usually pressurised from the air pressure in a compressed air receiver into which the compressor delivers its air output. When the compressor stops after a period of running, it is desirable to stop the continued flow of oil under pressure into the compressor which would otherwise overfill the compressor.

According to the present invention, in an oil-flooded air compressor having an oil system for supplying a flow of lubricating and cooling oil under pressure to the compressor, the oil system being pressurised from a source of pressure which remains effective after the compressor has stopped running, and including a shut-off valve for controlling the flow of pressurised oil to the compressor, the shut-off valve comprises a valve body formed with a bore affording intercommunicating large-diameter and small-diameter bore portions, and a valve spool slidable longitudinally in the bore between open and closed operative positions, the spool having a head which is a close sliding fit in the large-diameter bore portion and having a hollow stem which is a close sliding fit in the small-diameter bore portion, the interior of the hollow stem of the spool at its end remote from the head being open and in permanent communication with an inlet in the valve body connected to the oil system for the entry of the pressurised oil flow and being closed at its other end, and the hollow stem having a port or ports formed in and extending through the thickness of its side wall, there being an outlet from the valve body connected to the compressor and the said port or ports being in communication with the outlet by movement of the valve spool into its open position, but being shut off from the outlet when the valve spool is in its closed position, whereby the flow path for the pressurised oil flow from the inlet to the outlet when the spool is in its open position is via the open end of the hollow stem into its interior and thence via the said port or ports to the outlet from the valve body, the said flow path being shut off when the spool is moved into its closed position, and there being a control port leading into the large-diameter bore portion and communicating with the compressor delivery outlet to admit the delivery air pressure of the compressor into the large diameter bore portion to act on the head of the spool so as to open and hold the valve against the force of the oil pressure at the inlet when the compressor starts running and continues to run, allowing the flow of oil through the valve to the compressor, whereas when the compressor stops and its delivery pressure falls the valve is closed automatically to stop the oil flow by the residual oil pressure acting on the stem of the valve spool.

The closing of the shut-off valve when the compressor stops is preferably effected solely by the residual pressure of the oil at the inlet acting on the valve spool without spring assistance.

Thus the valve opens automatically in response to the admission of the delivery air pressure to the large-diameter bore portion, and is closed automatically and preferably solely by the pressure of the oil supply to its inlet, when the delivery air pressure fails on the stopping of the compressor.

The small-internal bore portion may be formed with an internal circumferential groove communicaing with the valve body outlet, the ports or ports in the side wall of the hollow spool stem opening into this groove when the spool is in the open position, but being closed by the wall of the small-diameter bore portion when the spool is in its closed position.

The invention may be carried into practice in various ways, but one specific embodiment thereof will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a longitudinal sectional view of a shut-off valve, and Figure 2 is a diagram showing the valve of Figure 1 incorporated in the oil system of an oil-flooded air compressor.

The valve 10 shown in Figure 1 comprises a valve body 11 formed with an axial inlet 12 at one end for the flow to be controlled, and a radial outlet passage 13 in its side for the discharge of the flow to be controlled. In its other end the valve body 11 has a screw plug 14 in which is formed a control port 15. The valve body has a longitudinal cylindrical bore extending between its opposite ends, the bore comprising a large-diameter bore portion 16 closed at its outer end by the screw plug 14, and a small-diameter portion 17 whose outer end constitutes the inlet 12 and is tapped to receive an oil pipe connection. An intermediate step portion 18 is provided between the two bore portions 16 and 17.The bore portion 17 has an internal circumferential groove 19 in its wall at an intermediate position in its length, and the radial outlet passage 13 in the valve body 11 communicates with the groove 19.

A longitudinally movable valve spool 20 is slidable in the bore in the valve body. The spool has a head 21 which is a close sliding fit in the large-diameter bore portion 16, and a hollow open-ended stem 22 which is a close sliding fit in the small-diameter bore portion 17 (the clearances between the spool and the bore are exaggerated in the drawings).

Radially-facing Ports 23 are formed in the side wall of the hollow stem 22 and extend through the wall from its interior bore 25 to its external cylindrical surface. The ports 23 communicate with the groove 19 when the valve is in its open position shown in Figure 1, with the back 21A of the spool head 21 abutted against the step 18. A vent passage 26 extends through the valve body 11 to vent the space 27 in the large-diameter bore portion 16 behind the spool head 21 to the exterior of the valve body. When the spool is moved towards the left in Figure 1 from its open position to its closed position, its head seats against an annular sealing surface 28 formed on the plug 14, and the radial ports 23 are closed by the internal surface of the wall of the left-hand portion of the small-diameter bore portion 17.

In use in its application to the control of the oil flow for an oil-flooded air compressor, the valve 10 is connected in the compressor circuit as shown diagrammatically in Figure 2.

Thus, the compressor 30 which is of intermeshing-screw type, has an air intake 31 and a delivery line 32 for compressed air leading to a combined air receiver and oil reservoir 33.

The receiver/reservoir 33 has an oil separator and reclaimer 34A to which is connected the air output connection 34 of the receiver. An oil delivery pipe 35 leads from the lower part of the reservoir 37 and contains oil subject to the air pressure in the receiver 33. The oil delivery pipe 35 is connected to the inlet 12 of the valve 10, and the valve outlet 13 is connected to the high-pressure oil inlet 38 of the compressor. A vent line 39 connects the vent passage 26 to a low-air-pressure region of the compressor casing. The used lubricating and cooling oil from the compressor 30 is discharged with the compressed air delivery through the air delivery line 32, to the receiver 30 where it rejoins the oil supply in the reservoir 37.

The control pressure is provided by the pressure of the compressed air output of the compressor 30, and a control line 41 connects a point on the air delivery line 32 to the control port 15 of the valve 10. A non-return valve 32A is fitted in the line 32 beyond the control line 41.

Thus, in use, when the compressor 30 is working its air delivery pressure constituting the control pressure is admitted to the large-diameter bore portion 16 of the valve to act on the head 21 of the valve spool 20 to hold the spool pressed against the step 18 in its open position as shown in Figure 1, so that oil under pressure from the reservoir 37 can flow into the inlet 12, through the bore 25 of the hollow stem 22 and out through the radial ports 23 to the outlet 13 and thence to the inlet 38 in the compressor casing. The abutment of the back 21A of the spool head 21 against the step 18 seals the bore portion 16 against the escape of the compressed air from the control line 41. Because the control pressure air acts on the large-diameter head of the valve spool 22, it will overcome the oil pressure in the oil delivery pipe 35 at receiver pressure acting on the small-diameter radial surfaces of the valve stem, and will hold the spool in its open position, even if the oil pressure at the valve inlet 12 equals the compressor delivery pressure as might be the case if the compressor were started up while air/oil pressure remained in the system. Any oil seeping past the valve stem 22 into the space 27 behind the spool head 21 will be vented via the vent passage 26 to the low-pressure region of the compressor.This prevents the space 27 from becoming filled with oil, which would interfere with the working of the valve When the compressor is stopped, the air delivery pressure collapses in the delivery line 32, reducing the control pressure in the chamber 16 so that the force on the head 21 holding the valve spool in its open position is removed. The residual air pressure in the receiver 30 will act, via the oil delivery pipe 35, on the stem 23 and will move the spool 20 to the left in Figure 1 in its closed position in which the ports 23 are covered and closed by the wall of the bore portion 17 and the main flow path through the valve from inlet 12 to outlet 13 is shut off, thus preventing the compressor from being filled with oil under the action of the residual pressure in the receiver/reservoir 33.

In its application to the oil flow of an oil-flooded air compressor, the valve 10 does not require seals on its valve spool. The valve is extremely simple and inexpensive in its construction and employs no springs or diaphragms. It comprises only a single moving part, namely the valve spool.

WHAT WE CLAIM IS: 1. An oil-flooded air compressor having an oil system for supplying a flow of lubricating and cooling oil under pressure to the compressor, the oil system being pressurised from a source of pressure which remains effective after the compressor has stopped running and including a shut-off valve for controlling the flow of pressurised oil to the compressor, in which the shut-off valve comprises a valve body formed with a bore affording intercommunicating large-diameter and small-diameter bore portions, and a valve spool slidable longitudinally in the bore between open and closed operative positions, the spool having a head which is a close sliding fit in the large-diameter bore portion and having a hollow stem which is a close sliding fit in the small-diameter bore portion, the interior of the hollow stem of the spool at its end remote from the head being open and in permanent communication with an inlet in the valve body connected to the oil system for the entry of the pressurised oil flow and being closed at its other end, and the hollow stem having a port or ports formed in and extending through the thickness of its side wall, there being an outlet from the valve body connected to the compressor and the said port or ports being put in communication with the outlet by movement of the valve spool into its open position, but being shut off from the outlet when the valve spool is in its closed position, whereby the flow path for the pressurised oil flow from the inlet to the outlet when the spool is in its open position is via the open end of the hollow stem into its interior and thence via the said port or ports to the outlet from the valve body, the said flow path being shut off when the spool is moved into its closed position, and there being a control port leading into the large-diameter bore portion and communicating with the compressor delivery outlet to admit the delivery air pressure of the compressor into the large-diameter bore portion to act on the head of the spool so as to open and hold open the valve against the force of the oil pressure at the inlet when the compressor starts running and continues to run, allowing the flow of oil through the valve to the compressor, whereas when the compressor stops and its delivery pressure falls the valve is closed automatically to stop the oil flow by the residual oil pressure acting on the stem of the valve spool.

2. A compressor as claimed in Claim 1, in which the closing of the valve when the compressor stops is effected solely by the residual pressure of the oil at the inlet acting on the valve spool.

3. A compressor as claimed in Claim 1 or Claim 2, in which the small-diameter bore portion is formed with an internal circumferential groove communicating with the valve body outlet, the port or ports in the side wall of the hollow spool stem opening into this groove when the spool is in its open position, but being closed by the wall of the small-diameter bore portion when the spool is in its closed position.

4. An oil-flooded air compressor having a valve-controlled lubrication system substantially as specifically described herein with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. started up while air/oil pressure remained in the system. Any oil seeping past the valve stem 22 into the space 27 behind the spool head 21 will be vented via the vent passage 26 to the low-pressure region of the compressor. This prevents the space 27 from becoming filled with oil, which would interfere with the working of the valve When the compressor is stopped, the air delivery pressure collapses in the delivery line 32, reducing the control pressure in the chamber 16 so that the force on the head 21 holding the valve spool in its open position is removed.The residual air pressure in the receiver 30 will act, via the oil delivery pipe 35, on the stem 23 and will move the spool 20 to the left in Figure 1 in its closed position in which the ports 23 are covered and closed by the wall of the bore portion 17 and the main flow path through the valve from inlet 12 to outlet 13 is shut off, thus preventing the compressor from being filled with oil under the action of the residual pressure in the receiver/reservoir 33. In its application to the oil flow of an oil-flooded air compressor, the valve 10 does not require seals on its valve spool. The valve is extremely simple and inexpensive in its construction and employs no springs or diaphragms. It comprises only a single moving part, namely the valve spool. WHAT WE CLAIM IS:

1. An oil-flooded air compressor having an oil system for supplying a flow of lubricating and cooling oil under pressure to the compressor, the oil system being pressurised from a source of pressure which remains effective after the compressor has stopped running and including a shut-off valve for controlling the flow of pressurised oil to the compressor, in which the shut-off valve comprises a valve body formed with a bore affording intercommunicating large-diameter and small-diameter bore portions, and a valve spool slidable longitudinally in the bore between open and closed operative positions, the spool having a head which is a close sliding fit in the large-diameter bore portion and having a hollow stem which is a close sliding fit in the small-diameter bore portion, the interior of the hollow stem of the spool at its end remote from the head being open and in permanent communication with an inlet in the valve body connected to the oil system for the entry of the pressurised oil flow and being closed at its other end, and the hollow stem having a port or ports formed in and extending through the thickness of its side wall, there being an outlet from the valve body connected to the compressor and the said port or ports being put in communication with the outlet by movement of the valve spool into its open position, but being shut off from the outlet when the valve spool is in its closed position, whereby the flow path for the pressurised oil flow from the inlet to the outlet when the spool is in its open position is via the open end of the hollow stem into its interior and thence via the said port or ports to the outlet from the valve body, the said flow path being shut off when the spool is moved into its closed position, and there being a control port leading into the large-diameter bore portion and communicating with the compressor delivery outlet to admit the delivery air pressure of the compressor into the large-diameter bore portion to act on the head of the spool so as to open and hold open the valve against the force of the oil pressure at the inlet when the compressor starts running and continues to run, allowing the flow of oil through the valve to the compressor, whereas when the compressor stops and its delivery pressure falls the valve is closed automatically to stop the oil flow by the residual oil pressure acting on the stem of the valve spool.

2. A compressor as claimed in Claim 1, in which the closing of the valve when the compressor stops is effected solely by the residual pressure of the oil at the inlet acting on the valve spool.

3. A compressor as claimed in Claim 1 or Claim 2, in which the small-diameter bore portion is formed with an internal circumferential groove communicating with the valve body outlet, the port or ports in the side wall of the hollow spool stem opening into this groove when the spool is in its open position, but being closed by the wall of the small-diameter bore portion when the spool is in its closed position.

4. An oil-flooded air compressor having a valve-controlled lubrication system substantially as specifically described herein with reference to the accompanying drawings.