GB2133117A - Double diaphragm valve - Google Patents

Abstract

To prevent stall of an aircraft engine, in a fail-safe diaphragm valve A having an upper chamber 41 fed by a pressure switch C with a calibrated pressure fluid, a lower chamber 40 fed by a control fluid from a compressor, and a double-beat piston 10, diaphragms 2,2' define an intermediate chamber 42 in constant communication with atmosphere or a low pressure source whereby should one or both of the diaphragms 2,2' develop a leak, the piston 10 will not close on to lower seat 7 and hence compressor air valve B will not close. <IMAGE>

Description

SPECIFICATION Double diaphragm valve This invention consists in a doubie diaphragm pneumatic valve, to be inserted into the intput of an actuator, which in turn opens, respectively shuts an air valve from the compressor to the atmosphere, with an anti-stall functions at the lowest speed rates. The invention is alternatively as in Claim 5.

It is known that in modern aircraft engines the comburant air is compressed in a turbo compressor, before going forwarded to the combustion chamber.

At the lowest engine speed rates, the air flow through the final compressor stages is choked in such a way that only a fraction of it completes the compression and is then let into the combustion chamber; this is done by means of an air valve controlled by a proper pneumatic actuator using as driving fluid the compressed air flowing out of said compressor.

The need to do so derives from the fact that the profiles of the compressor bladings being normally designed for maximum power, when the speed is lower there might occur particular transient stall conditions (detachment of the nappe from the profiles) with consequent incorrect engine running.

Discharging a part of the air externally, at the lowest speed rates, a reduction of the axial speed of the nappe is obtained, with consequent reinstatement of incidence angles compatible with a correct engine running.

More generally, the pneumatic valve according to the invention accomplishes the following: a) Receiving a calibrated signal from a calibrable pressure clutch it permits or discontinues, depending respectively on whether the input signal is higher or lower than a given value, the passage of end compression air (P2 Pressure) to an actuator which in turn shuts, respectively opens a compressor air valve into the atmosphere, with anti-stall function at the lowest speed rates.

b) It cuts away, and discontinues the spreading into the flow of fluctuation and unstableness originated in the pressure switch and present in the signal, which would otherwise cause high frequency cyclings on the'air valve, with premature wearout and incorrect running.

c) It reacts to failures (perforations and cuts) of one or both diaphragms by taking such a position as to cause the permanent opening of the compressor air valves at all speed rates, thus establishing the safest trim to prevent stalls; this is the "Fail Safe" characteristic, and what the invention consists of: in having devised a particular way of using the flexible diaphragms on a relay pneumatic valve of this type, so that the breaking or damaging the said diaphragms cannot cause any shutting in the air valve, with negative consequences on the engine safe running (stall conditions).

Indeed, the regular diaphragm relay valves essentially consist of two chambers (separated from each other by the diaphragm); the end of compression pressure P2 acts on one of them, whereas the signal pressure KP2 acts on the other; in case of perforation of the diaphragm, the P2 pressure breaks into the other chamber, pressurizing it and generating a closing signal with consequent piston positioning, so as to cause the closing of the compressor air valve. As will be specified hereinafter, the new valve is so devised that possibie air leaks through the diaphragms may become exhausted into the atmosphere through the proper ducts provided for in the chamber between the two diaphragms, and therefore they do not pressurize the signal pressure chamber KP2.

Therefore, there will be no closing signal, and the valve will continue to be in the open air escape position.

The essential characteristics of the invention are schematically summarized in the appended claims; its objects and advantages will further appear from the following specification, with particular reference to the attached drawings, wherein: - Figures 1/A and 1/B are longitudinal sections of diaphragm valve (A) according to the invention, in two different positions, respectively open and closed, and their relevant connections with air valve (B) on the compressor, and with a pressure switch (C) generating a pilot signal.

- Figure 2 is a longitudinal section of the valve according to the invention, positioned so as to determine the opening of the air valve on the compressor; - Figure 3 is a section similar to that shown in Figure 2, with the difference that it shows the diaphragm valve according to the invention in a position apt to determine the closing of the air valve on the compressor; - Figure 4 is a longitudinal section of the diaphragm valve according to the invention, shown with the upper diaphragm perforated, and positioned so that, in spite of this, it determines the opening of the air valve on the compressor;; - Figure 5 is a longitudinal section of the diaphragm valve according to the invention, shown with the lower diaphragm perforated and positioned so that, in spite of this, it determines the opening of the air valve on the compressor.

- Figure 6 is another longitudinal section of the diaphragm valve according to the invention, shown with both diaphragms perforated, and positioned so that, in spite of this, it determines the opening of the air valve on the compressor.

In Figures 1/A and 1/B reference letter A identifies the diaphragm valve according to the invention which is fed via duct 14, by the compressed air originated from the compressor diffuser (not shown).

The said duct 14 feeds the lower chamber 40 of the diaphragm valve (A) with the air compressed at pressure (P2).

The upper chamber 41 of the diaphragm valve A is fed, via duct 19, by a pressure switch (C), with a calibrated control pressure (KP2) proportional to pressure (P2) originated from the compressor which causes the lowering of the diaphragm valve shutter only when pressure (P2) from the upper compressor exceeds a predetermined level; such is indeed the function of the above said pressure switch (C).

In a way per se known, pressure switch (C) receives on one side pressure (P2) whereas it is connected on the other side to the atmospheric pressure (P1).

When chamber 47 of air valve B is fed via duct 46 by the pressure (P2) existing in the lower chamber 40 of the diaphragm valve (as shown in Fig. 1/B), piston 31 and shutter 32 connected thereto are pushed downwards, so as to close the air orifice 48 which connects the compressor to the atmosphere in a section related to one of the iast stages (or to the last stage).

In Figures 1/A and 1/B, reference number 48 identifies the above said orifice.

When piston 10 of diaphragm valve A is raised (as shown in Fig. 1/A) chamber 47 of air valve B is in communication with the atmosphere via ducts 46 and 45, and orifice 44; shutter 32 of air valve B is raised by the air pressure acting on the lower surface, hence orifice 48 is in communication with the atmosphere, thus allowing the compressor air to escape outwardly.

Thus far the behaviour of the diaphragm valve and its connection to pressure switch (C) on one hand and to air valve B on the other hand are similar to that of conventional single diaphragm valves. Indeed, when both diaphragms of a diaphragm valve are unimpaired the latter behaves as if it were a single diaphragm valve, provided with an unimpaired diaphragm.

Let us now see in detail how the diaphragm valve works.

On the upper side of body 4 of diaphragm valve A according to the invention there is assembled the unit consisting of two diaphragms 2 and 2', separated from each other by spacers 29 and 30, and tightened against body 4 of lid 6 to form three distinct chambers: upper chamber 41 at pressure (KP2) fed by pressure switch (C) via duct 19, intermediate chamber 42 at atmospheric pressure (PO), and lower chamber 40 at pressure (P2) fed by duct 14 connected to the compressor outlet.

Lower chamber 40 can be closed downwards on the upper seat 4' of head 10' when piston 10, of which it is a part and through which it is connected to diaphragms 2 and 2', is pushed upwards. Via passages 44, ducts 45 and 46, hence chamber 47 of air valve B, are put in communication with the atmosphere.

When head 10' of piston 10 is engaged against lower seat 7, chamber 40, wherein there is pressure P2, communicates, via channelings 45 and 46, with chamber 47 of air valve B, thus causing a shift downwards of piston 31 and of shutter 32 connected thereto, and the closing of the said valve.

The whole is completed by union connectors, respectively nO 1 9 for calibrated pressure (KP2) acting as pilot signal, nO 14 for pressure (P2), besides the previously mentioned nO 45 for connection with air valve chamber B.

In regular working conditions, with unimpaired diaphragms (see Figures 1/A and 2), and stationary engine, the valve diaphragms are on two parallel planes, and the valve seat is in an intermediate position between beat 4' upwards and beat 7 downwards on the flange seat.

When the engine starts, the end of compression air P2 first discharges through lower opening 44 toward the atmosphere, then, when pressure P2 attains a given value, which for the manufactured valve specimen is for example 1.3 Kg/cm2i, the resultant force on the diaphragm is such as to cause their shift upwards, which causes head 10' of piston 10 with beat on upper seat 4' to close chamber 40; in these conditions, the air under pressure cannot reach chamber 47 of air valve B, piston 31 remains in a raised position and the air valve remains open.

When, at given pressure valve P2, pressure switch C trips and releases a signal KP2, the latter reaches upper valve chamber 41 and, the various surfaces involved being suitably calibrated, it determines a resultant downwards acting on the assembly of diaphragms which then push head 10' to beat on lower seat 7, thus determining the channeling of P2 towards chamber 47 of air valve B, piston 31 shifts and shutter 32 closes compressor discharge orifice 43.

It is sufficient for the end of compression pressure to descend below the calibrated value for pressure switch C to discontinue signal KP2 to chamber 41, which leads to the fact that the force generated by P2 is no longer counter-balanced, and consequently there is a quick shifting of the head, which is dragged by the diaphragm, via the piston, to cover upper seat 4'. This leads to the interruption of the flow of air P2 to chamber 47, to put it in communication with the atmosphere, via hole 44 in flange 7, and then to let the air valve open under the action of the compressor pressure.

Therefore, the valve behaves as if it were a single diaphragm valve of KNOWN TYPE.

In case upper diaphragm 2 is perforated (see Fig. 4), at very low speeds (namely when P2 is < 1.3 Kg/cmZ and at speed rates lower than the closing point provided for, when there is no KP2 signal on the upper chamber) the valve behaviour is entirely similar to that of a valve in normal working conditions. At the moment the pressure switch supplies a KP2 signal to the upper chamber, the air of this signal is not retained by upper diaphragm 2, which is perforated, and leaks through the hole in the said diaphragm, then passes on to chamber 42, and thererom, via ducts 43, to the atmosphere. The consequence is that chamber 41 is not pressurized, no downwards force is exerted, and the valve remains preconditioned for the opening of air valve B throughout the engine running area.

Let us now examine how the valve works when the lower diaphragm is perforated (see Fig. 5).

At very low.speed rates, the valve remains in the intermediate position of the head for a slightly longer period of time. This slight delay is due to pressure reduction in chamber P2, caused by air leakage through the hole of diaphragm 2' into chamber 42, and hence through ducts 43 into the atmosphere.

Above a given speed rate, head 10' is pushed upwards against upper seat 4' with a force, however, which is insufficient for it to keep sealed.

For this reason, the valve remains in the said position, with plenty of air discharge into the atmosphere through hole 44 of flange 7 throughout the remaining engine running area.

Also when signal KP2 starts working at a given speed rate, it only causes a greater breakaway of head 10' from the upper seat and a greater discharge of P2 into the atmosphere, with consequent impossibility for signal P2 to reach air valve chamber 47. Therefore, the valve keeps air shutter 32 in a raised position throughout the engine running area.

Let us now consider how the valve works when both diaphragms are perforated (see Fig. 6).

In these conditions there is essentially a discharge of signal P2 into the atmosphere at slow speed, which weakens chamber P2 pressure to the point that the upwards shift of head 10' is not big enough to keep the upper seat sealed. When speed increases conditions remain unchanged also with the coming in place of signal KP2, which goes out into the atmosphere through holes 43 and leaves the valve with the head in an intermediate position with consequent discharge into the atmosphere through both channels 43 and hole 44 of flange 7.

It is clear that in these conditions P2 does not extend over piston 31, and the air valve on the engine remains open.

Although for the description purposes this invention is based upon the embodiments specified above, by way of example only, with particular reference to the appended drawings, many modifications and variants can be made in the invention embodiment; said modifications and variants having however to be considered as based on the following claims.

Claims (5)

1. A diaphragm valve of the type providing for an upper chamber fed by a pressure switch with a calibrated pressure fluid, lower chamber fed by a control fluid, preferably originated from a compressor diffuser, a shutter movable between two positions, wherein in correspondence with the first position, namely when the force generated by the control fluid in the said lower chamber, an actuator cylinder is put in communication with a low pressure source preferably the atmosphere, whereas in correspondence with the second position, namely when the force generated by the control fluid in the upper chamber prevails, the said actuator is put in communication with the high pressure source, preferably the lower chamber of the diaphragm valve, charácterized in that the said diaphragm valve provides for two diaphragms one above the other, and essentially parallel, between which there is defined an intermediate chamber constantly in communication with the said low pressure source, preferably the atmosphere.

2. A diaphragm valve according to the preceding claim, characterized in that the said lower chamber is via a passage crossed with clearance by the shutter rod, in communication with a distribution chamber, which is in turn in communication with a cylinder of the said pneumatic actuator; and/or with a low pressure source: said actuator consisting of a head-shaped valve body which, when the force generated by the control pressure in the upper chamber prevails, closes a passage port between the said distribution chamber and the low pressure source, thus allowing for the passage of the pressurized fluid from the said lower chamber to the said actuator cylinder; wherein, alternatively, when the force generated by the control fluid pressure prevails in the lower chamber, the said shutter closes the passage port between the said lower chamber and the distribution chamber, a passage port being then open between the said distribution chamber and the said low pressure source, namely the atmosphere.

3. A diaphragm valve according to the preceding claims, characterized in that the control of the said actuator causes the closing of an atmosphere discharge valve of the last stage or diffuser of an aircraft engine.

4. A diaphragm valve according to the preceding claims, substantially embodied and operated according to the previous specification and illustrations, by way of example only, with particular reference to the appended drawings.

5. A diaphragm valve having a first duct for connection to a source of control pressure, a second duct for connection to a slave valve, and a third duct for connection to a source of working pressure, the diaphragm valve having a first valving position in which the second duct is put in communication with the third duct and a second valving position in which the second duct is vented or put in communication with a low pressure, and the diaphragm valve comprising first and second spaced diaphragms defining an intermediate chamber between the diaphragms, the intermediate chamber being vented or in communication with a duct for communication with low pressure, a first main chamber on the other side of the first diaphragm, in communication with the first duct, and a second main chamber on the other side of the second diaphragm, in communication with the third duct, whereby the diaphragm valve assumes the first valving position or the second valving position in accordance with the relative values of the control pressure and the working pressure.