GB2258717A

GB2258717A - Air compressor surge protection system

Info

Publication number: GB2258717A
Application number: GB9217340A
Authority: GB
Inventors: Michael John Zaple; Christopher Francis Roots; Donald James Richards
Original assignee: NORMALAIR GARRETT
Current assignee: NORMALAIR GARRETT
Priority date: 1991-08-16
Filing date: 1992-08-14
Publication date: 1993-02-17
Also published as: GB9217340D0; GB9117781D0; FR2680394A1

Abstract

An air compressor surge protection system provides a direct acting vent valve 18 giving rapid response to flow conditions which may give rise to compressor surging by opening the valve to vent to ambient compressed air flowing in a delivery duct 10 thereby preventing the onset of surging. A venturi 11 is connected in line with the delivery duct. Static pressure differential in the venturi is sensed and used to drive a pneumatic actuator 20, 21, 22 for control of movement of the vent valve which is biased to an open position by a compression spring 28. <IMAGE>

Description

Description of Invention AIR COMPRESSOR SURGE PROTECTION SYSTEM This invention relates to air compressor apparatus which in operation delivers a flow of compressed air and is more particularly concerned with a system for preventing the onset of compressor surge due to throttling back of the delivery flow.

Air compressors are used to supply compressed air for a variety of purposes, the flow of compressed air usually being delivered by way of a duct. One such example is found in ground equipment employing a high speed bladed air compressor to supply compressed air to start the gas turbine engines of an aircraft. In the event of a restriction downstream of the compressor which acts to throttle back the delivery flow, such as may occur following engine start up, the airflow over the compressor blades becomes unstable giving rise to compressor surging which may be damaging to the equipment.

It is an object of the present invention to provide a system for preventing the onset of compressor surge in operation of air compressor apparatus.

Accordingly, in one aspect the present invention provides a system for preventing onset of compressor surge in air compressor apparatus which in operation supplies a flow of compressed air to an air delivery duct, comprising a venturi located in the delivery duct, vent valve means downstream of the venturi for communicating the delivery duct with ambient atmosphere, means for biasing the vent valve means to an open position when there is zero airflow through the venturi, and pneumatic actuator means responsive to static pressure differential in the venturi for moving the vent valve means progressively towards a closed position with increasing airflow through the venturi.

In operation of the system static pressures in a venturi inlet section and a venturi throat section are sensed and a differential in these pressures is used to drive the pneumatic actuator which together with the vent valve biasing means controls movement of the vent valve means between a closed position and an open position.

The static pressure differential is zero with zero airflow through the venturi and is a maximum when the airflow is a maximum. Consequently, an operating band of airflow between compressor surge and maximum delivery can be translated into a venturi static pressure differential range for control purposes.

The vent valve means may comprise a valve member located internally of a vent duct having one end open to the interior of the compressed air delivery duct and an opposite end open to ambient.

Alternatively, the vent valve means may comprise a valved port located in a wall of the compressed air delivery duct downstream of the venturi.

The valve member may be any suitable valve such as, for example, a butterfly valve.

The pneumatic actuator means may comprise any suitable pneumatic actuator having actuator piston means connected with the vent valve means and adapted for sensing on one of its faces the static pressure at the venturi throat section and on its opposite face the static pressure at the venturi inlet section.

The means for biasing the vent valve means to a fully open position may comprise resilient means such as, for example, a compression spring provided with the pneumatic actuator means.

A system in accordance with the present invention has direct acting vent valve means giving rapid response to throttling back of system airflow in venting system air to prevent onset of compressor surge, and is particularly suited for use in any apparatus which uses a bladed air compressor to deliver a flow of air at increased pressure.

Accordingly, in another aspect the invention provides apparatus for delivering a flow of compressed air, comprising an air compressor having an ambient air inlet and a compressed air outlet, a compressed air delivery duct having one end connected to the compressor outlet, a venturi connected in line with the delivery duct, vent valve means connected in the delivery duct downstream of the venturi including a valve member adapted for movement between a closed position and an open position, means for biasing the valve member to the open position, pneumatic actuator means including actuator piston means, means for connecting the actuator piston means with the valve member, means connecting an inlet section of the venturi with one face of the actuator piston means and means connecting a venturi throat section with an opposite side of the actuator piston means, whereby in operation with air flowing through the venturi a static pressure differential between the venturi inlet section and the venturi throat section is operative to move the actuator piston means and with it the valve member towards the closed position in opposition to the valve member biasing means.

The actuator piston means may comprise a conventional piston adapted to slide internally of a cylinder or it may comprise any other suitable piston means such as, for example, a plate member carried by a diaphragm member which is attached to and supported by an internal wall of a cylinder.

The apparatus may be, for example, a gas turbine engine starter trolley or ground based environmental control apparatus for delivering conditioned air to the interior of a building.

The invention will now be further described by way of example only and with reference to the accompanying drawing which schematically depicts a system in accordance with one embodiment of the invention.

A compressed air delivery duct 10 has one end connected to an outlet of a high speed bladed air compressor (not shown) and its other end connected for delivering air to an appliance requiring a supply of compressed air such as, for example, an aircraft gas turbine engine (not shown). Connected in line with the duct 10 is a venturi 11 having an inlet section 12, a throat section 13 and an outlet section 14.

Vent valve means which in this embodiment comprises a vent duct 15, is connected with the delivery duct 10 downstream of the venturi outlet section 14. The vent duct has one end 16 open to the interior of the delivery duct 10 and an opposite end open to ambient atmosphere. The vent valve means further comprises a valve member which in this embodiment comprises a butterfly valve 18 pivotally mounted on a spindle 19 internally of the vent duct 15.

Pneumatic actuator means for moving the butterfly valve 18 from a fully open position to a closed position comprises a cylinder 20 housing actuator piston means which in this embodiment is provided by a plate member 21 carried by a diaphragm member 22 attached to and supported by an internal circumferential wall of the cylinder. The plate member 21 and diaphragm member 22 serve to divide the cylinder 20 into two chambers 24 and 25. An actuator rod 26 extends from attachment to that side of the plate member 21 which faces the chamber 25 and projects externally of the cylinder 23 to connect with one end of a link member 27 having its opposite end connected to the butterfly valve member 18.

The butterfly valve member 18 is biased to a fully open position by resilient means which in this embodiment comprises a compression spring 28 housed in the chamber 25 and acting between an end wall of the cylinder 20 and the plate member 21.

A conduit line 29 connects between the venturi throat section 13 and the chamber 25 and a conduit line 30 connects between the venturi inlet 12 and the chamber 24 whereby in operation the static pressures in the venturi inlet section and the venturi throat section are conveyed to either side of the diaphragm supported plate member, and air is able to flow to charge/discharge the actuator chambers to achieve actuator movement.

In operation of the system with the air compressor (not shown) non-operational there is zero airflow through the venturi 11 and the butterfly valve member 18 is biased by the spring 28 to the fully open position so that the delivery duct 10 is communicated with ambient atmosphere by way of the vent duct 17. In this condition the static pressures in the venturi inlet section 12 and throat section 13 are the same and the pressure differential in the chambers 24 and 25 of the cylinder 20 is zero.

For a given total pressure, static pressure falls with increasing flow, thus for constant total pressure, as flow goes up, static pressure comes down. Total pressure at the venturi throat section is substantially the same as total pressure at the inlet section, there being negligible loss of total pressure in the contracted throat section.

Thus as airflow through the delivery duct 10 and venturi 11 builds up following start-up of the air compressor, the rate of change of static pressure with flow is greater in the venturi throat section 13 than in the venturi inlet section 12 and a venturi static pressure differential is created which is a maximum when the flow is a maximum. Since for constant total pressure static pressure falls with increasing airflow, the static pressure sensed in the chamber 25 falls at a higher rate than that sensed in the chamber 24 and a pressure differential is built up across the plate member 21 and diaphragm member 22, which is effective to move the butterfly valve progressively towards the closed position in opposition to the compression spring 28.At maximum flow conditions the pressure differential is such that the butterfly valve completely closes the vent duct and the total flow of the compressed air in the delivery duct is to the appliance requiring the supply.

Should a restriction occur downstream of the venturi at maximum flow giving rise to throttling back in the delivery flow, the total pressure rises due to the compressor characteristic; however, a change in the venturi inlet section static pressure is matched by a change in the throat section static pressure except that the change in the latter is at a different rate. Thus the static pressure differential changes such that the compression spring 28 acts to move the butterfly valve 18 towards opening so that compressed air in the delivery duct 10 is dumped to ambient atmosphere through the vent duct 15 and the onset of compressor surging is prevented.

The system of the present invention has direct acting vent valve means giving rapid response to flow conditions which may give rise to compressor surging by opening the vent valve means to vent compressed air from the delivery duct to ambient thereby preventing the onset of surging. Biasing the vent valve means to an open position in zero flow conditions provides a safety feature in the event that a restriction to flow is present on start up of the air compressor which would otherwise cause throttling back of the delivery flow resulting in compressor surging. By locating the vent valve means downstream of the venturi airflow from the compressor is vented to ambient until a pneumatic signal appropriate for driving the pneumatic actuator means to close the vent valve means is generated when there is satisfactory flow through the venturi. In addition to the prevention of compressor surge due to throttling back of the delivery flow, the surge protection system also caters for complete shut down of the delivery flow line, either expected or unexpected, whilst the compressor is still being driven.

Claims

CLEMS

1. A system for preventing onset of compressor surge in air compressor apparatus which in operation supplies a flow of compressed air to a delivery duct, comprising a venturi located in the delivery duct, vent valve means downstream of the venturi for communicating the delivery duct with ambient atmosphere, means for biasing the vent valve means to an open position when there is zero airflow through the venturi, and pneumatic actuator means responsive to static pressure differential in the venturi for moving the vent valve means progressively towards a closed position with increasing airflow through the venturi.

2. A system according to Claim 1, wherein static pressures in a venturi inlet section and a venturi throat section are sensed and a differential in these pressures is used to drive the pneumatic actuator means which together with the vent valve biasing means controls progressive movement of the vent valve means between an open position and a closed position.

3. A system according to Claim 2, wherein the pneumatic actuator means comprises an actuator piston connected with the vent valve means, the actuator piston being adapted for sensing static pressure in the venturi throat section on one of its faces and static pressure at the venturi inlet section of its opposite face.

4. A system according to any one of the preceding claims, wherein the vent valve means comprises a valve member located internally of a vent duct having one end open to the interior of the compressed air delivery duct downstream of the venturi.

5. A system according to Claim 3, wherein the valve member comprises a butterfly valve.

6. A system according to any one of the preceding claims, wherein the biasing means comprises a spring loading the pneumatic actuator means.

7. Apparatus for delivering a flow of compressed air, comprising an air compressor having an ambient air inlet and a compressed air outlet, a compressed air delivery duct having one end connected to the compressor outlet, a venturi connected in line with the delivery duct, vent valve means connected in the delivery duct downstream of the venturi including a valve member adapted for movement between a closed position and an open position, means for biasing the valve member to the open position, pneumatic actuator means including actuator piston means, means for connecting the actuator piston means with the valve member, means connecting an inlet section of the venturi with one face of the actuator piston means and means connecting a venturi throat section with an opposite side of the actuator piston means, whereby in operation with air flowing through the venturi a static pressure differential between the venturi inlet section and the venturi throat section is operative to move the actuator piston means and with it the valve member towards the closed position in opposition to the valve member biasing means.

8. A system for preventing the onset of compressor surge substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

9. Any new or improved features, combinations and arrangements described, shown or mentioned or any of them together or separately.