What are the main types of flow control for liquids?
Flow-control valves can be simple orifices or complex closed-loop electrohydraulic valves, which automatically adjust to changes in temperature and pressure. The aim of flow control is speed regulation. Besides that, the flow rate will determine the rate of energy-transfer at a set pressure. The correlation between these two is this: actuator force x distance = work done to load. Energy transfer must be equal to work done. The actuator speed thus determines energy transfer. As such, speed varies according to the rate of flow. If you would like further detailed information regarding industrial liquid flow systems see flow efficient for latest information.
Here are the types of flow control:
A simple orifice is the simplest method to control flow. When controlling flow, the orifice and the pump will be in series. It can be as simple as a hole drilled in a fitting, which is usually fixed. Alternatively, it may be a needle valve that is calibrated, working as the variable orifice. Both of these work as non-compensated valves.
- Flow regulators
This valve is more complex than a fixed orifice. The orifice will sense the flow rate as pressure drops across the orifice. There is a piston, which will compensate for variations in outlet and inlet pressures. The control accuracy can be 5% or less with calibrated valves designed to work around a dedicated flow rate point.
- Bypass flow regulators
The flow that is in excess of the set flow rate goes back to the tank via a bypass port. The flow rate is controlled via throttling fluid across a variable orifice that is regulated using a compensator piston. It is a more efficient design that the standard regulator.
- Demand-compensated flow controls
In this setup, the fluid will be diverted to the main circuit at a controlled rate of flow. This fluid is often utilized for work in secondary circuits with no effect of the main circuit. The valve only functions when flow to the main circuit is maintained. Flow in the whole system stops if flow to the main circuit is cut.
This setup is fitted with a variable orifice and compensator that are in series. The compensator will automatically adjust to the varying inlet and load pressure. It helps to maintain a constant flow rate to an accuracy of 3%-5%. These valves come with an integral reverse flow check valve that allows fluid to flow without restrictions in the opposite direction. Besides that, an integral overload relief valve will route fluid to a tank once maximum pressure is reached.
- Pressure/temperature-compensated flow
Since hydraulic oil viscosity changes with temperature, as will the clearance between the moving parts of the valve, the output of flow control valves could drift as temperature changes. To offset this effect, a temperature compensator will adjust the openings of the control orifice to correct for these effects of changes in viscosity due to temperature variations. This is done in conjunction with adjustment to the control orifice for changes in pressure.
- Priority valve
In this setup, the flow control valve supplies fluid at a set rate to the main circuit. As such, it works in the same way as compensated flow valves, which are a pressure-compensated. A flow that exceeds what is needed in the main circuit will be passed on to an auxiliary circuit at a lower pressure than the main circuit. Should the load or inlet pressure vary, the main circuit takes priority over the secondary circuit in terms of supplying the flow rate.
- Deceleration valves
It comes as a customized 2-way spring-counterbalanced valve that is cam actuated. It is used to decelerate a load being driven by the cylinder. A cam that is fixed to the load or cylinder will close the valve slowly. It provides a variable orifice, which cause a slow rise in the cylinder’s backpressure as the valve closes. Some of these deceleration valves also feature pressure compensation.