Piston Digital Control Valve is an electrically actuated, hydraulically operated multi-function control valve. It can be used for local as well as remote controlled batching operations with electronic batch controller. The valve also offers an in-built flow governing function.
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DESIGN FEATURES

• Precision multi-stage opening & closing.
• Fail-safe design.
• Low Pressure Drop.
• Bubble-tight seat design.
• Flow Rate Control.

PRINCIPLES OF OPERATION

The Piston Valve basically consists of a spring loaded piston, sliding in the guide liner, & two solenoid valves. Normally open (NO) solenoid connects the chamber above the piston to the upstream pressure, whereas normally closed (NC) solenoid connects the chamber above the piston to the downstream pressure. Operation of the Piston Valve is simple & is explained below.

Piston is always exposed to high upstream pressure from its bottom side, whereas pressure above the piston (forming a closed chamber with the cover) can be varied with the help of solenoid valves.

Initially both NO & NC solenoid valves are in de-energised condition. The NO solenoid applies high upstream pressure on top side of the piston, whereas the NC valve prevents this pressure from getting drained to the downstream side. The valve remains close as a result of this.

When both NO & NC solenoid valves are energised, the pressure from above the piston starts draining to the downstream side. This creates a differential pressure across the piston, the high upstream pressure acting from below the piston pushes it up in the liner, which allows the flow to gradually start through the valve.

If NC solenoid valve is de-energised anytime, it stops draining of pressure above the piston & therefore the valve locks at the current flow rate.

When both NO & NC solenoid valves are de-energised, high upstream pressure is applied over the piston, which pushes it down to close completely over the valve seat to achieve bubble-tight shut-off.

Using an electronic batch controller, the opening & closing of the valve can be digitally controlled & can be made into multiple stages.

Rate of Flow Control

When a number of flow meters are connected to the same pump, stopping (or starting) one or more meters increases (or decreases) the flow rate at the remaining meters. When the flow rate increases, the NO solenoid is energised momentarily. This injects some high pressure over the piston & makes the valve to throttle, in order to maintain the set flow rate. If the flow rate decreases, the NC solenoid is energised momentarily. This allows slight draining of of the pressure & allows the valve to open further in order to maintain the set flow rate.

Note The number of stages during opening & closing are programmed in the batch controller & can be as many as desired. One stage during opening & two during closing are recommended.

APPLICATIONS

• Road Tanker & Rail Wagon gantry filling.
• Custody Transfer & Inventory Control
• Batching, Blending & Dispensing in petroleum, petro-chemical & process control industries.

OPTIONS

• Piston Valve can be supplied with flameproof Limit Switches to give electrical signal to annunciator regarding the valve position - open or closed.
• Standard Valve is supplied with 230 V AC solenoids, other voltage solenoids can be supplied on request.