NO315438B1 - Device at constant flow valve - Google Patents

Description

CONSTANT FLOW VALVE DEVICE

This invention relates to a constant flow valve, more specifically a constant flow valve for use in dosing fluids, for example chemicals in connection with petroleum extraction.

Constant flow valves of the kind in question here must be built to be able to dose small amounts of fluid with great accuracy, even if significant pressure variations occur both on the upstream and downstream side of the valve.

US patent 4,893,649 deals with a constant flow valve comprising two flow regulating elements. The first flow-regulating element consists of a fixed nozzle, a so-called throttle valve, of the type where the flow rate is dependent on the pressure drop across the nozzle. The second flow-regulating element is a needle valve which is arranged to maintain a constant pressure drop across the fixed nozzle.

The regulation principle from the device according to the above-mentioned US patent is also found in other known constant current

ning valves.

According to known technology, the fluid pressure in the inlet of the constant flow valve acts on a regulating piston connected to the valve needle of the needle valve in such a way that the needle valve is closed. Fluid flows through the throttle valve to a chamber on the opposite side of the regulating piston, where it exerts pressure against the regulating piston. The fluid pressure against the regulating piston's chamber side, together with the force from a valve spring, displaces the valve needle from the needle valve seat so that fluid is drained out of the chamber. The needle valve can then close again. By regulating the force from the valve spring, for example by means of biasing, the pressure drop across the throttle valve can be regulated.

When connecting a constant flow valve to a relatively high fluid pressure, a significant force will be exerted against the piston's closing side before a sufficient amount of fluid to fill and equalize the pressure flows through the throttle valve. The needle valve's valve needle is thus often exposed to damage by crushing since hard, brittle materials are used. It is therefore common for constant flow valves according to known technology to be provided with a spring-loaded attachment of the valve needle in the regulating piston.

The regulation piston's seal against the valve housing gives rise to frictional forces during the constant flow valve's regulation which can significantly influence the constant flow valve's accuracy. It has also been shown that the valve needle's springy attachment to the regulating piston can lead to inaccurate regulation, as the valve needle's relative displaceability in relation to the regulating piston acts as a disturbance.

Known constant flow valves' valve spring preload control devices also complicate and make the valves unnecessarily expensive.

The purpose of the invention is to remedy the disadvantages of known techniques.

The purpose is achieved according to the invention by the features indicated in the description below and in the subsequent patent claims,

By supplying a constant flow valve with an adjustable throttle valve, it is possible to achieve a wide regulation range without having to regulate the bias of the constant flow valve's needle valve opening valve spring.

The dosing accuracy is significantly improved by the fact that the valve needle of the needle valve is displaced by a diaphragm. The valve needle regulation is thereby not disturbed by seal-related friction. Experiments have shown that a constant flow valve according to the invention exhibits such a high degree of repetition accuracy that the constant flow valve's throttle valve in a preferred embodiment is provided with a vernier scale to facilitate the setting of, for example, a previously calibrated flow rate.

Damage to the valve needle is prevented by placing an elastic material with a relatively small height between the valve needle and the diaphragm, for example in the form of a so-called O-ring. The length of the valve needle is adapted in such a way that the valve needle, when it is in its closed position, does not protrude against the membrane when the membrane is completely displaced in the direction of the valve needle. The space between the valve needle and the diaphragm is occupied by the elastic material mentioned above.

The operation of the constant flow valve is explained in the special part of the description.

In what follows, a non-limiting example of a preferred embodiment is described which is illustrated in the accompanying drawings, where: Fig. 1 shows a section of a constant flow valve; Fig. 2 shows on a larger scale a section of the needle valve in fig. 1, the needle valve being in an open position; and Fig. 3 shows the same as fig. 2, but here the needle valve is in a closed position.

In the drawings, the reference number 1 denotes a constant flow valve comprising an upper housing part 2, a lower housing part 4, a throttle valve 6 and a needle valve 8. A membrane 10 is sealingly placed in a recess 12 between the housing parts 2 and 4, see fig. 1 and 2.

The housing upper part 2 is provided with an inlet 14 for the fluid to flow through the constant flow valve 1, from which an inlet channel 16 connects the inlet 14 to the inlet chamber 18 of the throttle valve 6. From the inlet chamber 18, a channel 20 extends to the recess 12 and opens onto the closing pressure side 22 of the diaphragm 10, see fig. 3.

A bore 24 runs concentrically with the throttle needle 26 of the throttle valve 6 from the inlet chamber 18 to the lower housing part 4, where it continues through the lower housing part 4 and to the needle valve 8. A gasket 28 prevents leakage between the housing parts 2 and 4 from the bore 24.

The throat needle 26 is designed with a conical end portion which projects into the bore 24, and the throat needle 26 is arranged to be displaced out and into the bore 24 by means of a regulation part 30 of a known design per se.

The membrane 10 is firmly clamped between the housing upper part 2 and the housing lower part 4 by means of bolts not shown. Gaskets 32 in the form of O-rings prevent leakage between the housing parts 2 and 4 from the recess 12, see fig. 2.

A needle valve bore 34 extends concentrically with and from the recess 12 and into the housing lower part 4 to a shoulder part 36 from which an outlet channel 38 extends to the outlet 40 of the constant flow valve 1.

A needle valve seat 42, which is provided with a through bore ring 44, is placed in the needle valve bore 34 and lies sealingly, by means of a gasket 46, against the shoulder part 36.

A valve needle guide 48 is placed in the needle valve bore 34 and connected to the lower housing part 4 by means of a threaded connection 50. The end surface 52 of the valve needle guide 48 facing the upper housing part 2 is essentially level with the recess 12 of the lower housing part 4. The valve needle guide 48 is provided with a through bore 54. The bore 54 is further drilled out closest to the end surface 52 so that a shoulder 56 is formed in the bore 54. A valve needle/closing body 58 is displaceably placed in the bore 54 of the valve needle guide 48 with sufficient clearance so that an annular space is formed through which fluid can flow between the valve needle 58 and the bore 54. The valve needle 58 is externally provided with a shoulder 60, and with a conical sealing surface 62 in its end part facing the needle valve seat 42. An 0-ring 64 is placed between the opposite end part 66 of the valve needle 58 and the membrane 10.

A helical valve spring 68 extends between the abutment 56 in the valve guide 48 and the abutment 60 of the valve needle 58 and is designed to displace the valve needle 58 in the direction out from the needle valve seat 42.

Fluid from the bore 24 can flow into the needle valve 8 through recesses 70 in the needle valve guide 48.

When it is opened so that fluid under pressure can flow into the inlet 14 of the constant flow valve 1 and further through

the inlet channel 16 to the inlet chamber 18, the closing pressure side 22 of the membrane 10 is exposed to full fluid pressure after a short time via the channel 20. The valve needle 58 is displaced via the O-ring 64 with a relatively large force towards the needle valve seat 42, see fig. 3. Meanwhile, the end part 66 of the valve needle 58 is displaced to a level slightly below the end surface 52 of the valve guide 48 before the sealing surface 62 closes against the needle valve seat 42. The membrane 10 is thus prevented from coming into contact with the end part 66 of the valve needle 58, and the closing force of the valve needle is thus limited to the closing force that is transmitted via the relatively soft O-ring 64. There is therefore no danger that the valve needle 58 can be crushed by the closing force from the membrane 10.

Fluid then flows through the throat valve 6 and into an annular gap that is formed between the throat needle 26 and the bore 24 and then further through the bore 24 and the recess 70 until

life valve 8.

Some fluid flows past the valve needle 58 and into the recess 12. The fluid pressure against the two sides of the diaphragm 10 is equalised, so that the relatively weak valve spring 68 can displace the valve needle from the needle valve seat 42, whereby fluid can flow through the bore 44 and the channel 38 to the constant flow valve 1's outlet race 40.

The supply of fluid to the needle valve 8 is limited by the throttle valve 6. When a larger amount of fluid is drained from the needle valve 8 than is supplied through the throttle valve 6, the pressure in the needle valve 8 drops. The force from the fluid pressure difference between the two sides of the membrane 10 thereby overcomes the force from the valve spring 68, as that the needle valve 8 closes.

By adapting the relationship between the dimension of the diaphragm 10 and the force of the valve spring 68, it is possible to achieve a very accurate pressure drop regulation, as there is only negligible friction between the valve needle guide 48 and the valve needle 58. The deflection of the diaphragm 10 is also not affected by frictional forces.

With a constant pressure drop across the throttle valve 6, the fluid flow through the constant flow valve 1 for a specific fluid at a specific temperature essentially only depends on the throttle valve 6's opening. Tests have shown that the constant flow valve's 1 repetition accuracy is very good.

Claims (3)

1. Device for constant flow valve (1) of the kind where a second valve (8), for example in the form of a needle valve, is designed to maintain a constant pressure drop across a first valve (6), for example a throttle valve, characterized by that the second valve's (8) closing body (58) is arranged to be displaced towards its closing position by a fluid pressure-affected membrane (10) via an elastic material (64). 2. Device according to claim 1, characterized in that the closing body (58) against. the part (66) facing the membrane (10) is at a distance from the membrane (10) when the membrane (10) is fully extended in the direction of the closing body (58) and the closing body is in its closed position. 3. Device according to one or more of the preceding claims, characterized in that between the closing body (58) and the closing body's (58) guide (48) there is an annulus of sufficient opening for fluid to flow through the annulus.