GB2239935A

GB2239935A - A fluid flow rate limiter

Info

Publication number: GB2239935A
Application number: GB9100253A
Authority: GB
Inventors: Maurice Tardy
Original assignee: FABRICATION ET D ETUDES DE COM
Current assignee: FABRICATION ET D ETUDES DE COM
Priority date: 1990-01-15
Filing date: 1991-01-07
Publication date: 1991-07-17
Anticipated expiration: 2011-01-07
Also published as: FR2657140B1; GB9100253D0; ITMI910033A0; FR2657140A1; IT1245082B; ITMI910033A1; GB2239935B; DE4100231A1

Abstract

The flow rate limiter consists of a body (1) containing a circular bore, one end (2) of which is closed whilst the other end (4) is open and connected to a hydraulic appliance, and having an internal tubular slide (5) of circular cross-section guided axially in the bore and displaceable under the influence of a pressure difference acting in opposition to the constraints exercised by the fluid, the middle portion of the slide (5) having a machined annular groove (7) into which there open two axially staggered rings of orifices (8, 9) machined in the body (1), and the slide also having two compartments separated by an intermediate shoulder (12) in a manner such that the compartment (10) towards the closed end (2) of the body (1) communicates with the annular groove (7) through at least one bore (13) and contains a valve (14) acted upon by resilient means (20) which urge it against the shoulder in the direction of controlled fluid flow, further resilient means (17) being provided to exert on the slide a pressure in the direction of the closed end of the body. The arrangement provides free movement of fluid from (4) to (8) under pump pressure and controlled movement of fluid from (8) to (9) when the pump is inoperative. <IMAGE>

Description

1 - A fluid flow rate limiter The present invention relates to a fluid

flow rate limiter. The term fluid flow rate limiter denotes any device capable of regulating the flow rate of a fluid with compensation for pressure fluctuations. Devices of this nature usually consist of an' automatic fluid flow rate limiting valve, adapted on the one hand to allow the fluid to flow in a given direction up to a pressure level corresponding to a prescribed threshold value, without significantly hindering the stream, and on the other hand to maintain a constant flow rate irrespective of the pressure load.

Fluid flow rate limiters of this nature are widely used wher- ever it is required to provide a supply of fluid at a specified flow rate irrespective of the system pressure.

Thus for example flow rate limiters are notably but not exclusively used as valves to reduce the discharge rate from single-acting hoist cylinders when descending under load.

Such flow rate limiters, functioning as described, allow the regulation of fluid flow rates by acting as a stream control valve with regulation of the live section in the direction of opening and/or closure. At the equilibrium fluid flow rate, the pre-set closure force and the hydraulic force set up by the pressure drop are in balance.

There already exists a number of known types of fluid flow rate limiters. In general, the valve member consists of a hollow piston which controls the live section of the valve de- vice by means of a control ridge formed in its skirt, and which itself carries a metering diaphragm comprising an orifice in k the piston crown, so adapted that on the one hand fluid flows through the hollow piston itself and on the other hand the meter ing diaphragm can be moved as part of the piston.

In the direction of uncontrolled fluid flow there is thus no limitation of the fluid flow rate, but merely a maximum aperture.

In this direction, the pre-set closure force acting on the valve member is superimposed on the resistance to the passage of the fluid stream.

This type of control is found to be indispensable in the case of fluid flow rate limiters in which the diaphragm acts as a metering orifice.

In fact, it is found that when the fluid circulates in the inverse direction, i.e., in the direction of uncontrolled fluid flow, the fluid is controlled instantaneously by virtue of the balancing of the pressure difference, which spontaneously falls as soon as the valve device is opened.

However, this type of fluid flow rate limiter has the draw back of undergoing serious overheating as a result of the brak ing resistance opposing the opening of the diaphragm in the direction of uncontrolled fluid flow.

This problem is usually remedied by fitting a check-valve in parallel, to act as a fluid limitation valve. The said valve is closed in the direction of controlled fluid flow and open in the direction of uncontrolled fluid flow.

On the other hand, the provision of such a valve involves both an increase in the equipment space requirement and an addition to the equipment costs. Furthermore, when the equip ment is subjected to high pressures, the check-valve is found 1 to be poorly adapted to sustaining such working loads It is known to users of fluid flow rate limiters, but not exclusively in situations where the devices to high working pressure loads, to resort to the use of fluid flow rate limiting valves in which the live section of the orifice, in the direction of uncontrolled fluid flow, matically displaced into a position of free passage, larging the live section of the diaphragm orifice in independent 6f the valve device.

It is thus known in this type of flow rate limiter to connect an adjustable member forming a choke-valve for the metering orifice with a valve component which can be adjusted as a function of the positions of the member. The adjustment of this valve is thus effected by means of delimited bearings.

It is also possible to provide the displaceable member of the metering diaphragm, which is usually a diaphragm with orifices, with a retaining spring, or even to leave it freely floating. In every case, and with a view to ensuring an effective limitation of fluid flow rates, it is preferable for the displaceable 20 member to be guided within the valve component of the device.

However, such flow rate limiters are usually very complicated in design, difficult to maintain an-d often highly expensive.

Moreover, they only allow adjustment of the live section of the valve into certain specific positions, in the case of 25 uncontrolled fluid flow.

Finally, in the case where a by-pass channel is provided in the direction of uncontrolled fluid flow it is difficult to connect the displaceable member to a component controlling the live section of the by-pass channel.

notably are subiected diaphragm can be autothereby ena manner The present invention is intended to remedy these problems by providing a flow rate limiter which allows the ready passage of fluids both in the direction of controlled fluid flow, by virtue of using appropriately shaped mechanical components, and in the direction of uncontrolled fluid flow. It is moreover simple to operate, very robust and quite easy to service.

Accordingly, the proposed fluid flow rate limiter allowing the passage of a fluid under pressure both in the direction of controlled flow and in the direction of uncontrolled flow con- sists of a body containing a circular bore, one end of which is closed whilst the other end is open and connected to a hydraulic appliance, and housing aninternal tubular slide of circular cross-section guided axially in the bore and displadeable under the influence of a pressure difference acting in opposition to the constraints exercised by the fluid, the middle portion of the slide having a machined annular groove into which there open two axially staggered rings of orifices machined in the body, and the slide also having two compartments separated by an intermediate shoulder in a manner such that the compartment disposed towards the closed end of the body communicates with the annular groove through at least one bore and contains a valve acted upon by resilient means which urge it against the shoulder in the direction of controlled fluid flow, further resilient means being provided to exert on the slide a pressure in the direction of the closed end of the body.

This fluid flow rate limiter allows the slide automatically to take up a position which ensures constant equilibrium between the constraints exerted by the pressures. In this way, the variations in the ruling external pressure at the inlet to the flow rate limiter in the direction of controlled flow no longer influence the pressure set up,et the open end of the limiter on the one hand and at the closed end on the other hand.

By virtue of the specific dispositions of the Valve and the slide in the direction of uncontrolled fluid flow, the fluid flow rate limiter parts the fluid stream, allowing a certain proportion to flow through the annular groove and the remaining significantly larger proportion to flow through the tubular s 1 i d e.

Moreover, the circular section of the slide is adapted to Sustain on the one hand the constraint exercised by the pressure at the level of its open end and on the other hand at the level of its closed end.

Thus, if 5 is the section of the slide, P2 the pressure ruling at the level of its closed end and P3 the pressure ruling at the level of its open end, the pressures P2 and P3 each generate a force determined as follows: for the pressure P2, a closure force given by the formula P2S; for the pressure P3, an opening force given by the formula P 3 5.

Equilibrium is defined by the equation P2S = P3S + To, where To denotes the opening force exerted by a coil spring which holds the slide in its control position.

Hence the pressure difference is P2 - P3 1-0, where To is the S opening force exerted by the coil spring in holding the slide in its control position, To being the characteristic spring constant.

The pressure difference in the orifice disposed downstream 1 6 - of the supporting member on which the fluid flow rate limiter is mounted remains constant, and for a given live section s the fluid flow rate Q remains constant at:

2 2(P2 - P3) P: density; V_ P Y 4: load loss factor- Thus, the fluid flow rate limiter ensures the maintenance of a constant fluid circulation, and particularly by virtue of its annular groove promotes regular and uniform streamlining in the directions of both controlled and uncontrolled flow.

According to one interesting feature of the invention, at least one bore machined radially through the wall of the tubular valve body allows a certain amount of fluid to enter the valve in the direction of the closed end of the body.

The head of the valve in axial section is preferably sub- stantially U-shaped, the parallel sides each being terminally chamfered so that they abut against the shoulder of the slide in the direction of controlled flow.

This abutment of the valve in the direction of controlled flow ensures the closure of the bore machined in the slide, so that fluid can only enter through the bore machined in the body of the valve.

According to another interesting feature of the invention, the resilient means holding the slide in position consist of a coil spring abutting against the slide at one end and a washer at the other.

The washer supporting one end of the coil spring which holds the slide in position is preferably secured in the body with the aid of a split ring.

This arrangement keeps the spring in contact with the slide 1 and with the body, thereby ensuring good adaptation of the position of the slide which permits correct regulation of the fluid flow rate with pressure compensation.

According to a further characteristic of this preferred embodiment of the invention, the resilient means holding the valve in its position-consist of a coil spring abutting against the valve at one end and a washer at the other.

The washer supporting one end of the valve holding spring is preferably attached mechanically to the slide. This attachment ensures that the fluid flow rate limiter will be perfectly leak- proof.

According to another interesting feature of the invention, the body is threaded over the middle section between the two rings of orifices, so that it can be set up in a suitably tapped mount.

Every aspect of the invention will be fully disclosed in the following description of the annexed schematic drawing of a typical embodiment thereof, purely by way of non-limiting example.

Figure 1 shows an axial section through the limiter of the invention, in a rest position, Figures 2 and 3 are similar views to Figure 1, showing the positions for fluid flow in the controlled and uncontrolled directions respectively, Figures 4 and 5 show another embodiment, in axial section, in the controlled fluid flow position, and Figure 6 shows a section taken on the line IV-IV through Figure 4.

The flow rate limiter, best shown in its rest position in Figure 1, consists of a body 1 containing an internal circular bore, the one end 2 of which is closed by means of a nut 3 1 threaded to fit the internal thread in the bore. The other end 4 is open and can be connected to a hydraulic appliance not shown, for the sake of clarity, but consisting for example of the control compartment of a single-acting hoist cylinder in a load-lifting system.

The body I houses an internal tubular slide 5 of circular cross-section guided axially in the bore and displaceable under the influence of a pressure opposing the constraint exercised by the fluid. The middle portion of the slide 5 has an annular groove 7 into which there,.open two axially staggered rings of orifices 8, 9, approximately 3 mm in diameter, machined in the body. The slide 5 delimits two compartments 10, 11, separated by an intermediate shoulder 12 in a manner such that the compartment 10 disposed towards the closed end of the body communicates with the annular groove 7 through a series of machined holes 13.

A valve 14 inserted in the compartment 10 consists of a tubular body 15 and a head 16 of substantially U-shaped cross-section, the parallel sides 16a each having a terminal chamfer 16b, so that they abut against the shoulder of the slide in the direction of controlled flow. The tubular body 15 has a bore 15b machined in its wall 15a, which allows a certain amount of fluid to enter the valve in the direction of the closed end 2 of the limiter.

A coil spring 17 abuts against the valve 14 at one end and a washer 21 at the other,- so that the valve 14 is held against the shoulder in the direction of uncontrolled fluid flow. The washer 21 is fixed mechanically in a manner that keeps the limiter leak-proof.

The body carries a thread 24 over its middle section between i c the two orifices 8,9, so that it can be set up in a suitable mount, and more particularly assembled into a complex hydraulic systems.

As shown more clearly in Figure 2, in the direction of controlled fluid flow the valve 14 is brought into a position in which it abuts against the shoulder 12 and is there held by the coil spring 20. The stream of fluid, notably but not exclusively oil under a high pressure, enters through the orifice 8 under a pressure P1, flows into the annular groove 7 machined in the slide 5 under a pressure P2 and emerges through the orifice 8 under a pressure P3, which exerts an opening force determined by the formula P3S on the surface of the open end 4 of the flow rate limiter. A certain amount of fluid subjected to the pressure P2 passes through the bore 15b machined in the body 15a of the slide 15 of the valve 14 and flows through the tubular - body 15 and across the washer 21 in the direction of the compartment 32 at the closed end 2 of the limiter, where it generates a closure force determined by the formula P2S.

In this way, and as already described in the preamble, the circulation of fluid generates a pressure difference (P2 - P3), so that when the closure and opening forces have reached equilibrium variations in the pressure rl will have no influence on those in the pressures P2 and P3, and consequently no influence on the fluid flow rate.

In equilibrium, the forces exerted by the pressures P2 and P3 on the surfaces of the open end and the closed end 2 of the limiter are opposed by the compression force on the spring 17. Hence, the slide 5 is displaced, the live section of the orifice 8 is reduced and as it were constricted until the balance is reached.

- However, it is important to note that the flow rate is a function of the cross-section s of the orifice 9 and the mechanical characteristics of the spring 17, and consequently the fluid flow rate can be adjusted to the needs of the system by a judicious choice of these variables, notably when the design and practical constructional parameters of the limiter are specified.

In the direction of uncontrolled flow, i.e., when the stream flows from the open end 4 of the body to its closed end 2, as shown best by Figure 3, the fluid is divided into two streams Q1 and Q2 of differing magnitudes. The first stream Q1 enters through the orifice 9, flows into the annular groove 7 and emerges through the orifice 8 as indicated by the arrow 22. The second stream Q2, which is more voluminous than the first stream Q1, passes through the axes of the washer 18 and the spring 17 and along the tubular slide 5, as shown more cleFarly by the arrow 23. This stream Q2 emerges through the orifice 13, which has been fully revealed by the displacement of the valve 14 under force exerted by the fluid pressure, into a retracted position in which it no longer abuts on the shoulder 12. The dynamic pressure of the fluid stream combined with the action of the spring keeps the valve 14 in this retracted position. The two fluid streams Q1 and Q2 merge at the level of the orifice 8 in a manner which maintains the circulation of fluid. A certain quantity of fluid undoubtedly still flows through the bore 15b machined in the body of the valve 14, along the inside of the tubular body 15, and through the washer 21 into the compartment 32 at the closed end 2 bf the limitbr.

It should be noted that hydraulic appliances of any and every kind, notably but not exclusively the control compartment of a "ZI the 11 load lifting cylinder, or any other hydraulic appliance requiring a specified and controllable supply Of 2CtU2ting fluid, can be connected to the described flow rate limiter, either at the open end 4 in the case requiring a controlled lifting action, or at the closed end 2 in the case requiring a controlled lowering action.

When the limiter is supplied with working fluid, usually oil under a high pressure, it allows a specified quantity of the fluid to pass through in unit time, thus bringing about.--controlled,laad '-d in the direction of lowering, whereas if the pressure is exet-uncontrolled flow an unlimited stream of pressurised oil will flow back into the cylinder and the load will be lifted. Thus the simple reversal from the direction of controlled flow to the direction of uncontrolled flow is all that is required to carry 15 out the operations of load lifting and load lowering.

This type of fluid flow rate limiter is generally used for working pressures of the order of 10 - 100 bar. Nevertheless, its use is not restricted to this range of working pressures.

Figures 4 and 5 show two alternative embodiments of the present fluid flow rate limiter.

Like features are referred to by like part numbers.

As shown in Figures 4 and 5, the fluid flow rate limiter can have a channel 27 communicating with two series of orifices 28, 29 in a manner whereby the annular groove 7 can be connected to the compartment 32 at the closed end 2 of the body 1.

The resilient means holding the valve 14 in its abutted position against the shoulder 12 consist of a coil spring 20 resting against the valve 14 at one end and a hood 33 at the other end.

In the direction of controlled flow, the fluid circulates in the direction indicated by the arrow 30 in the first variant of this embodiment shown in Figure 4, and in the opposite direction also indicated by the arrow 30 in the second variant of the same embodiment shown in Figure 5.

In these two embodiments, whether it be in the direction of controlled fluid flow or in the direction of uncontrolled fluid flow, a certain quantity of the fluid passes through the orifices 28, along the channel 27, through the orifices 29 and into the compartment 32 at the closed end 2 of the body 1 of the limiter.

The"invention is obviously not limited to the embodiments of the fluid flow rate limiter here described by way of nonrestrctive examples; it embraces all variants in execution and application which utilise the same principle.

w Q

Claims

1. A fluid flow rate limiter through which a fluid under pressure can flow alternately in the direction of controlled flow and the direction of uncontrolled flow, comprising a body containing a circular bore, one end of which is closed whilst the other end is open and connected to a hydraulic appliance, and housing an internal tubular slide of circular cross- section guided axially in the bore and displaceable under the influence of a pressure difference acting in opposition to the constraints exercised by the fluid, the middle portion of the slide having a machined annular groove into which there open two axially staggered rings of orifices machined in the body, and the slide also having two compartments separated by an intermediate shoulder in a manner such that the compartment towards the closed end of the body communicates with the annular groove through at least one bore and contains a valve acted upon by resilient means which urge it against the shoulder in the direction of controlled fluid flow, further resilient means being provided to exert on the slide a pressure in the direction of the closed end of the body.

2. A fluid flow rate limiter as in Claim 1, wherein at least one bore machined radially through the wall of the tubular body of the valve allows a certain amount of fluid to enter the valve in the direction of the compartment at the closed end of the body.

3. A fluid flow rate limiter as in either of Claims 1 and 2, wherein the head of the valve is substantially "U"- shaped, the parallel sides each being terminally chamfered so that they abut against the shoulder of the slide in the direction of controlled flow.

4. A fluid flow rate limiter as in Claim 1, wherein the resilient means holding the slide in position consists of a coil spring abutting against the slide at one end and a washer at the other.

5. A fluid flow rate limiter as in Claim 4, wherein the washer supporting one end of the spring which holds the slide "in position is secured in the body with the aid of a split ring.

6. A fluid flow rate limiter as in Claim 1, wherein the resilient means holding the valve, abutted against the shoulder, consists of a coil spring abutting against the valve at one end and a washer at the other.

7. A fluid flow rate limiter as in Claim 6, wherein the washer supporting one end of the spring holding the valve is attached mechanically to the slide.

8. A fluid flow rate limiter as in Claim 1, wherein the body is threaded over the middle section between the two rings of orifices, the thread being adapted to screw into a suitably tapped mount.

9. A fluid flow rate limiter as in Claim 1, incorporating a channel communicating with two series of orifices in a manner whereby the annular groove can be connected to the compartment at the closed end of the body.

10. A fluid flow rate limiter as in Claim 1, wherein the resilient means holding the valve in its abutted position j 4 is - against the shoulder consists of a coil spring resting against the valve at one end and a hood at the other end.

11. A fluid flow rate limiter substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

12. A fluid flow rate limiter substantially as hereinbefore described with referenc6 to Figures 4 to 6 of the accompanying drawings.

Published 1991 at The Patent 0111ce. State House. 66/71 High Holborn. LA)ndon WC I R 47P. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point. Cwmfehnfach. Cross Keys, Newport. NPI 7HZ. Printed by Multiplex techniques lid. St Mazy Cray, Kent.

MD UnLnUtI. UFUL Q. ni MUC MUIL. %,VMUC-AS- "'- -'Y" ---k- -Y - "-1"" --4"'- - --Y ---.Y, ---