Questions and Answers on Control Valves


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Read the general questions and answers on control valves. Control Valves technical questions and answers.

What is normal flow?

Normal flow through the main valve is described as “up and over the seat”. When valve is closing, it is against the flow and the forces are considered balanced.

What is reverse flow?

Reverse flow through the main valve is described as “over the seat and down”. When valve is closing it is with the flow and the forces are considered unbalanced.

When the main valve diaphragm wears out, the diaphragm assembly will go to the closed position (“fail closed”). This main valve option is primarily used with fueling valve applications and check valves.

How is two-way flow achieved?

Two-way flow is controlled using components in the pilot system, which allow the valve to control in both directions of flow through the main valve. Pilot controls can be different or the same in each flow direction.

A typical application of two way flow is the 210 Series Altitude valve. Here the term “two-way” is used to describe flow for applications where tank filling and discharge go through the same valve. The discharge flow from the tank often is referred to as “return” flow.

How is return flow achieved?

Return flow is controlled using components in the pilot system, which allow the valve to open whenever the inlet pressure is less than the outlet pressure.

Initially, the valve will be very slightly open at initial shift in pressure differential and will gradually go more open as the differential increases. This function overrides all other functions in pilot system. Components are same as check feature.

How can I quickly determine the head loss across a Automatic Pressure Reducing Valve?

The simplest way is to subtract the discharge pressure from the inlet pressure at a given rate. Pressure information can be easily accessed by equipping your Pressure Reducing Valve with the retrofittable Pressure Gauge on the inlet and outlet.

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