How can two pilots operate on one hydraulic control valve?

Recently, one of our customers asked how is it possible for two pilots to operate on the same hydraulic control valve without interfering with each other’s operation. In this short blog, we will describe how hydraulic flow control valves with two pilots operate.

Question

How can a single hydraulic control valve, equipped with two pilots, each with a totally different designated function, operate fulfilling the two functions, without the two pilots interfering with each other’s operation?

Note

The question and the following response were directed at BERMAD’s Flow Control & Pressure Reducing Valves, such as models IR-472-U, IR-172-d and IR-972-V, but can also be applied to any of BERMAD’s control valves which are equipped with two pilots or more.

Answer

BERMAD’s Flow Control & Pressure Reducing Valves are used in systems with high pressure on one hand, and a wide range of demand which can affect the supply system on the other hand. The Flow Control & Pressure Reducing Valves are installed in key points, such as consumer connection/offtake and function as follows:

• During periods where the demand is higher than the supply, the valves are required to limit the flow through them, to ensure an even water supply to all the consumers and to protect the supply system from significant drop in pressure
  
• During periods where the demand is lower than the design flow, the pressure will rise, even higher than the pressure rating of the pipes and accessories, so the valves are required to reduce the pressure

Another example where Flow Control & Pressure Reducing Valves are commonly used are gravity supply systems for multiple users located at various elevations. In these systems, the users located at lower elevations may consume more water, at the expense of the users located at higher elevations.

BERMAD’s Flow Control & Pressure Reducing Valves, such as models IR-472-U, IR-172-d and IR-972-V, are equipped with two different pilots, where one pilot is performing the Flow Limiting function and the second pilot is performing the Pressure Reducing function.

The following table and illustration are used as an example to demonstrate how the pilots, separately and together, control an IR-472-U Flow Control & Pressure Reducing Valve to open or throttle as required by the conditions in the system and the set points.

• The valve will open only when both pilots are open
• The valve will close when any one of the pilots is closed
• An open pilot is “giving” the control of the valve to the second pilot

IR-472-U  Control Diagram