Pumps – Condition responsive control of drive transmission or pump... – Adjustable cam or linkage
Reexamination Certificate
1999-07-06
2001-12-11
Tyler, Cheryl J. (Department: 3746)
Pumps
Condition responsive control of drive transmission or pump...
Adjustable cam or linkage
C137S115040, C137S115060, C137S115150
Reexamination Certificate
active
06328535
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a flow control valve, and in particular to a flow control valve having improved flow control characteristics resulting in improved output flow rates and pressures. The valve is particularly suited to pumps which pump fluids, predominantly containing liquids.
In a known pump assembly, the discharge from the pumping element flows to a valve arrangement having a valve element nominally floating in a bore. The valve arrangement includes a cavity into which the discharge from the pumping element flows. The cavity includes a discharge orifice through which fluid flows from the cavity with a pressure drop being established across the discharge orifice. The cavity has a further separate opening into the bore in which the valve element is “floating”. On the downstream side of the discharge orifice, a passage runs to the side of the bore, distant from the cavity, relative to the valve element. Thus, the valve element is balanced with two pressures, the pumping pressure (of the fluid in the cavity) acting on one end and the discharge pressure (determined by the discharge orifice) applied to the other end. A biasing member in the form of a spring is also provided to bias the valve element towards the cavity, whilst the pressure difference across the valve element acts to bias the valve element away from the cavity. In this way the valve arrangement is located in a bore which communicates across the discharge orifice of the cavity which in turn means that the valve element is separate from the discharge orifice.
In this arrangement, if the pumping pressure exceeds the discharge pressure by more than a predetermined amount, the valve element becomes sufficiently displaced from its position of zero displacement (i.e. its position when there is no pressure difference across the valve element) to open a channel to a spill port which directs fluid from the cavity back to the inlet of the pump. The difficulty with this arrangement is that there is insufficient control of the discharge flow rate, from the discharge orifice, with respect to pump speed and pressure. In fact, with such an arrangement, the discharge flow rate tends to increase with both pump speed and pressure.
The disadvantage described above with the conventional valve arrangement can be mitigated to an extent by forming a small recess in the front of the valve element and by suitable shaping of the spill port. Additionally, the valve arrangement may be improved by providing a “needle” (a rod having a profiled shape) on the end of the valve element which moves in the discharge orifice formed in a discharge plug aligned with the valve element, such that the annular area between the needle and the circumference of the discharge orifice varies with the movement of the valve element in the bore. The problems with this arrangement are that the needle position is fixed relative to the position of the valve element, the needle is expensive to manufacture and the region within the bore where the discharge pressure acts has an almost stagnant pool of fluid, where problems of contamination can develop. The valve element must also be further increased in complexity because of the need to incorporate within it a pressure relief valve, which opens at a high pressure setting (e.g. approximately 50-70 bars) to relieve pressure back to the pump inlet in the event of overloading the output.
SUMMARY OF THE INVENTION
The present invention seeks to provide a flow control valve which addresses the above identified disadvantages and provides an improvement over the prior art referred to.
According to the present invention there is provided a flow control valve comprising a body, a bore having first and second axial ends, the bore being formed within the body of the valve; a valve element movably located within the bore; an inlet in communication with the first axial end of the bore; an outlet in communication with the second axial end of the bore; adjustment means for adjusting at least one characteristic of the flow of fluid through the flow control valve in accordance with the position of the valve element within the bore; and a discharge orifice formed in the valve element for establishing a pressure differential across the valve element between the first and second axial ends of the bore.
With the present invention, therefore, the valve element, in combination with the discharge orifice in the valve element, provides the primary route through the valve to the outlet for discharging fluid, i.e. the main flow of fluid through the valve passes from the inlet into the valve element via the discharge orifice and out of the valve element via its open end to the outlet. This avoids the formation of stagnant “pools” of fluid either upstream or downstream of the valve element, as the majority of the fluid generally flows along the main axis of the flow control valve and is not diverted into a side channel.
The adjustment means preferably includes a spill port having an opening into the first axial end of the bore, the valve element being slidable axially within the bore between a first position, in which the opening of the spill port is blocked by the valve element, and a second position in which the opening to the spill port from the first axial end of the bore is not blocked by the valve element. In this way, a substantially constant pressure drop across the discharge orifice may be maintained.
Alternatively, or additionally, the adjustment means may include a needle which is positioned so as to project through the discharge orifice such that movement of the valve element within the bore causes relative movement between the discharge orifice and the needle which relative movement alters the clearance between the needle and discharge orifice. In this context, the needle functions as a variable closure member in relation to which the valve element and hence the discharge orifice move such that the relative movement between the valve element and the variable closure member alters the volume of fluid which flows per second through the discharge orifice. It is generally envisaged that the variable closure member will take the form of a shaped rod the external cross-sectional area of which varies along its length and which is mounted so that the free end of the rod projects through the discharge orifice such that relative axial movement between the valve element and the rod will cause the annular clearance between the rod and the discharge orifice to vary in size thus varying the volume of fluid which can flow through the clearance per second.
By mounting the needle so that the valve element (and thus, in the present invention, the discharge orifice) moves relative to it, there is much greater flexibility in the scope for design variations of the needle as it need not be attached to the valve element. For example, the needle may be rigidly fitted concentric or eccentric with the discharge orifice, it may be permitted to fall to one side of the discharge orifice to improve the consistency of flow restriction, or it may be mounted with flexibility axially and/or radially (with a device such as a spring, a pad or another valve) to increase the variables available for control of the rate of flow of fluid through the discharge orifice. There are also other advantages to the arrangement of the present invention such as the avoidance of the near stagnant area of fluid at the second axial end of the bore, and also, the needle is much cheaper and easier to manufacture. As the output or discharge of the flow control valve is straight through the discharge orifice in the valve element, no communication channel needs to be made to the second axial end of the bore from the downstream side of the discharge orifice, as is the case in the prior art, and so fluid and consequent pressure loss may be reduced.
By providing a small hole bored through the needle a safety pressure relief valve may be positioned in the closing plug or at any convenient location remote from the bore which senses the fluid pressure in the seco
Brighton Derek
Thornelow Alec
Hobourn Automative Limited
Tyler Cheryl J.
Wenderoth , Lind & Ponack, L.L.P.
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