Understand sequence valve design features, specification and performance limits.
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Tips for operating and maintaining
Sequence valves rely on consistent pressures to switch them at consistent points in the sequence. Pilot and main line pressure can however, be some of the more temperamental signals to control with. The actual pressure in any line will be dependent on the pipework size and length, including number of bends and small adaptors of fittings, fluid temperatures, fluid viscosity (condition), leakage (component wear), flow line pressure spikes (e.g. accelerating flow into the return line requires the mass of fluid to be accelerated, which will generate a higher line pressure) and what other actuators are operating at the same time.
It's always difficult to know what the exact pressure is inside a line, however, it's not unusual for local pilot flows, bypass flows or main system return flows to create significant local pressures or pressure peaks. It is important, when specifying a pressure sequence valve, to work out what the leakage and drain flows will be for each valve in the system. These values can be checked against the pipe sizes to make sure that local flows and pressure drops will not exceed or interact with the switching pressures.
It's not common for companies to publish the graphs for the range of pressures that their valve springs switch from one condition to another. For example, a valve may start to switch at 5 bar and finish switching at 10 bar. One company may quote the catalogue value for this valve as a 5 bar spring and another quote it as 10 bar spring. This probably won't make too much difference unless you have another pressure control valve that switches close to this pressure as well, and may induce and interaction between the two.
Again, catalogue values are quotes at particular operating conditions e.g. flow, temperature, pressure, viscosity etc. Some conversion value will need to be applied to these values if your system is working under different conditions.
Design features and operating characteristics
Sequence valves the design feature are similar to those of pressure relief valves and have already been covered in the