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Wednesday, 27 November 2013

Valves

Valves Points : Valves, Types of Valves, Pilot Valve, Relief Valve, Check Valve, Reverse Valve, Resistance Valve (foot valve), Control Valve The purpose of the valves is to control the flow of oils. The flow is through passages called ports; in through the suction (intake or inlet) port; out through the pressure (outlet) port.
Valves may be operated mechanically, electrically, or hydraulically, and for most actions may be automatic. Very sensitive valves for controlling the slightest movement (“inching “), even 0.00 1 in. of heavy tables, are not uncommon. Frequently two o more, and quite often several, valves are incorporated in the same hydraulic system.
Types of Valves 1. Pilot Valve Pilot valve is operated usually by dogs on a sliding table (or by hand) to release a comparatively small amount of oil to actuate some larger valve. 2. Relief Valve A relief valve may be adjusted to open at a predetermined pressure. 3. Check Valve A check valve permits a one-way flow only. 4. Reverse Valve A reverse valve is for the purpose of changing the direction of the flow of oil to the driven unit. 5. Resistance Valve (foot valve) It offers resistance in one direction of the flow. 6. Control Valve It may cover a variety of uses, .such as starting, stopping; speed changing, and quite often the movement of other valves for various purposes.

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