Control valve for controlling flow of hydraulic fluid

A control valve for controlling flow of hydraulic fluid, the control valve comprising:

• a valve housing;
• a sleeve slidable in a valve chamber in the valve housing;
• a first fluid conduit for connecting the valve chamber to a source of pressurised hydraulic fluid;
• a second fluid conduit for connecting the valve chamber to a fluid return for returning hydraulic fluid to a reservoir;
• a third fluid conduit for connecting the valve chamber to deliver hydraulic fluid to and receive hydraulic fluid from apparatus which uses the hydraulic fluid flow controlled by the control valve, wherein:
• the sleeve is a tubular sleeve having a tubular passage therethrough;
• the valve housing has a pair of spaced apart valve seat surfaces, a first valve seat surface which is engageable by a first annular end surface of the tubular sleeve and a second valve seat surface which is engageable by a second annular end surface of the tubular sleeve;
• the third fluid conduit opens on to the valve chamber by way of a port which is surrounded by the first valve seat surface;
• and
• when the first annular end surface of the tubular sleeve engages the first valve seat surface then fluid flows through the tubular passage in the sleeve from the third fluid conduit to the second fluid conduit and when the second annular end surface of the tubular sleeve engages the second valve seat surface then fluid flows through a gap between the first end of the tubular sleeve and the first valve seat to the third fluid conduit from the first fluid conduit;
• wherein:
• a spring means biases the sleeve into engagement with the first valve seat surface;
• characterised in that:
• the spring means acts directly on the sleeve;
• the tubular sleeve is connected by a rod to an armature located outside the valve chamber, the armature being located within an electrical coil also located outside the valve chamber;
• the spring means comprises a spring which acts between a spring seat provided in the valve housing and a spring seat fixed to the exterior of the sleeve;
• and
• the only forces applied to the rod are forces which place the rod in tension, the spring acting to move the sleeve into engagement with the first valve seat surface.