Flow control valve

A flow control valve comprising:

• a sleeve defining an inlet port open at the exterior thereof, an outlet port open at the exterior thereof, and an annular groove in the inner periphery thereof;
• a spool fitted in said sleeve, said spool and said sleeve defining a high pressure chamber at one end of the spool and a low pressure chamber at the other end of the spool, said spool having a portion between the ends thereof in a liquid-tight sliding engagement with the inner periphery of said sleeve, and said spool having a shoulder portion defining an annular groove in the outer periphery thereof;
• a fluid passage having a flow restriction orifice therein and extending between said high and said low pressure chambers;
• biasing means for biasing said spool in a direction opposite to that in which a force acts on the spool when pressure in the high pressure chamber exceeds that in the low pressure chamber;
• and
• an annular seal of soft resilient material liquid-tightly fitted in said annular groove in the inner periphery of said sleeve, said annular seal having an inner peripheral portion extending into said the annular groove in said spool with a gap therebetween,
• fluid communication between said inlet and said outlet ports through said orifice being established through said gap when the pressure differential at said ends of the spool is less than the force exerted on the spool by said biasing means, and said shoulder portion of said spool engaging said annular seal to effect a seal against said fluid communication when said pressure differential is greater than the force exerted on the spool by said biasing means, whereby the pressure differential at said ends of the spool is maintained at a value corresponding to the force exerted on the spool by said biasing means, and the flow rate of fluid between said inlet and said output ports is maintained at a value corresponding to the flow rate through said orifice.