Development of Sleeve and Spool Assembly of Hydraulic Spool Valve by Precision Engineering

Precision engineering involves not only manufacturing the components as per the design but also being able to measure and quantify them. This paper deals with the techniques and sequence of operations required for precision machining and metrological inspection of the components in the second- stage of a Hydraulic Spool Valve. The requirements of high accuracies in dimensions, form and surface quality are the prime requirements to meet the stringent valve specifications such as leakage, threshold, pressure gain, hysteresis, linearity etc. The sleeve and spool assembly of the spool valve forms the second stage of the valve. The sleeve is incorporated to meet higher flow requirements. It has many rectangular slots or flow openings. These slots are machined by Wire Cut Electrical Discharge Machining (WEDM) process. The spool has to be then machined to the dimensions obtained from the sleeve, in order to meet the required valve performance. This assembly has very critical clearance (between sleeve and spool), cylindricity and finish requirements. The paper presents the various precision machining techniques such as WEDM, cylindrical grinding, honing, and lapping used in achieving these requirements. These components have been assembled in the valve. The metrological and the valve performance results obtained have been given.