Fluid handling – Line condition change responsive valves – With separate connected fluid reactor surface
Patent
1993-10-13
1995-02-21
Nilson, Robert G.
Fluid handling
Line condition change responsive valves
With separate connected fluid reactor surface
1375133, F16F 934
Patent
active
053906969
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a pressure relief valve, particularly, but not exclusively, for an aircraft undercarriage damping arrangement.
An aircraft undercarriage arrangement is shown in FIG. 1 and comprises an upper leg 1 mounted at a suitable point in a wing of the aircraft, and a lower leg 2 slidably located about a lower end of the upper leg 1. The lower leg 2 is connected to a wheeled bogey by a trunnion 3. Upper leg 1 is hollow to define an upper cavity 4 whilst lower leg 5 defines a lower cavity is 5. The cavities are separated by an end wall 6 and the lower cavity is filled with a damping oil and the upper cavity filled with damping oil and nitrogen gas. The oil is allowed to flow through a valve 7 mounted in the end wall 6 to permit a controlled collapsing of the upper leg 1 into the lower leg 2, thereby absorbing the impact of landing.
In the event of a heavy landing, it is necessary for the valve 7 to open fully to "soften" the undercarriage and avoid the impact being transmitted to passengers. In the past this has been achieved by providing a valve 7 as shown in FIG. 2, with a spring-loaded orifice plate 8 which permits an initial limited flow through the orifice 9 therein, up to a predetermined pressure limit, at which the spring-loading is overcome and the plate lifts to allow an increased flow through the valve seat 8a with which the plate cooperates.
A problem with such existing valves is that the differential area of the orifice plate may be small at high operating pressures and the oil flow past it when the valve is open may prevent it from being held open in a positive manner.
According to the invention there is provided a pressure relief valve comprising a fluid flow channel through which an initial flow of fluid passes in use, and a valve opening member responsive at a predetermined fluid pressure to open the valve and allow an increased fluid flow therethrough, wherein the valve opening member is located substantially centrally in the fluid flow channel.
By locating the valve opening member substantially centrally in the fluid flow channel, said member is always exposed to the fluid flow, thereby making the valve more reliable in operation.
Preferably, the fluid flow channel is such as to reduce or eliminate any turbulent flow effects within the valve that would cause the valve opening characteristics to vary. In particular, the fluid flow channel is made long enough so that its outlet is spaced away from a fluid inlet port and associated valve member controlled by the valve opening member. Preferably, the region around the outlet end of the fluid flow channel is screened from the fluid inlet port and associated valve member. For example, the fluid flow channel may incorporate the valve member in the form of a valve seat at its inlet end which cooperates with the valve inlet so as to take all the flow through it when the valve is closed. An outer peripheral portion of the valve member may be guided within an outer housing and a screen may be provided around the outlet end of the fluid flow channel and the outer housing.
Preferably, the valve opening member is elongated in a direction substantially parallel to the axis of the fluid flow channel such that a valve opening force is exerted on it, induced by the drag of the fluid flow in the channel. This is preferable since the cross-sectional area of the valve opening member may be reduced producing a less turbulent fluid flow.
Conveniently, the valve opening member comprises a rod extending along the axis of the flow channel.
Preferably, the fluid flow channel is defined by part of the valve opening member. This is preferable because the drag generated by walls defining the fluid flow channel acts to open the valve permitting a further reduction in the cross-sectional area of the central portion of the valve opening member.
Advantageously, the fluid flow channel has substantially parallel walls to produce a substantially parallel fluid flow.
By producing a parallel fluid flow, turbulence is avoided which might produce a closing force on
REFERENCES:
patent: 2853159 (1958-09-01), Kuhn
patent: 3805825 (1974-04-01), Lovingham
patent: 4044791 (1977-08-01), McKenzie
Birch Brian D.
Bird Jeremy G.
Corfield Francis N.
Dowty Aerospace Gloucester Limited
Nilson Robert G.
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