Automatic Recycle Valve Technical Article

automatic recirculation valves start up

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Automatic Recirculation Valves Installation

17 May 2015/  /  in Automatic Recycle Valve Technical Article

Automatic recirculation valves Before start-up all lines must be flushed and the medium must be free from solids. Our valves are not designed to handle these. The lifetime of the valves will be strongly reduced due to increased wear when the fluid handled contains solids.

If the lines are not clean they can be flushed with the valves installed. This should however be done with the valve internals removed and at reduced pressures. Note that with the removal of the internals the non-return- and pressure letdown function are no longer present. After flushing the internals shall be reinstalled again. If the medium contains solids in the normal process we advice you to install a strainer with a mesh aperture of 0,25 to 0,5 mm in front of the pump inlet, because solids could block the movement of the valve internals.

Once the system is clean and filled with liquid the actual start-up can take place. The bypass line must have a guaranteed free flow path. This line should preferably not contain any valves except a non-return valve. If a gate- or ball valve is installed this valve should be locked in an open position. The process line must be lined-up as required. The pump can now be started as per pump manufacturers instructions. At the moment of start-up the bypass is fully open ensuring instant pump protection. By the time the pump reaches its operating point the bypass will be closed so that no energy is unnecessarily wasted with pumping around a minimum flow where the process flow covers the flow amount that is required to protect the pump. When the process flow drops below the minimum flow demand of the pump the bypass automatically opens allowing sufficient flow to keep the pump protected against overheating.

We advise to perform a functional test immediately after start-up as per following procedure:
Slowly reduce the main flow by closing the process line. When the process flow is reduced to the required pump minimum flow the bypass must start to open. When reducing the process flow further the bypass flow must increase. When the process line is closed a full bypass flow must be available.

Since our valves are self-containing there is no external stroke or flow indication. To check the bypass flow one needs a technical stethoscope (so that the bypass flow can be heard). In case of hot fluids one can measure the temperature rise of the bypass piping.

Now slowly open the process line again. The bypass flow must reduce. When the process line is fully open again the bypass flow is reduced to its minimum.

Another help to check the bypass flow is a manometer indicating the pump outlet pressure. There is a connection between pump flow and pump outlet pressure represented by the pump curve. Theoretically the pump pressure will never be higher than the pressure at full bypass flow (process line closed and bypass fully open). When the bypass line is blocked for whatever reason the pump pressure will increase above this pressure (max. up to shut-off pressure). The pressure at which the pump should run under normal- and under minimum flow conditions can be marked on the manometer. The pump should always operate on or between these two marks.

If the valve doesn't work as it should, immediately stop the pump to prevent eventual (further) damage. Check if the valve was installed correctly and if the process lines were lined-up properly. If this is the case the process conditions used for the valve-layout should be compared with the actual ones. When they are identical the problem might be within the valve itself. We advise to inspect the valve internals. Dirt or an object might have blocked the check valve movement

Note: The valve layout is based on specific flow- and pressure conditions. When one of these conditions is changed (e.g. a new pump is installed or another medium is transported) it influences the function of the valve. Before making any changes we shall be consulted to check on the possibly required valve changes.