Pressure control is the control of a fluid’s force within a vessel. It is transmitted equally in all directions. Think of your automobile’s tire pressure. When the pressure in all four tires is set properly, collectively they exert enough force (power) within, to safely support your automobile.
Flow control is controlling the movement of pressure between two vessels, and it moves from the vessel with greater pressure. When tire pressure is too high or too low, the tire valve is opened to release pressure from the tire “flowing” to the atmosphere or to receive a greater pressure “flowing” from the air compressor. Of course, a larger opening in the valve (or sadly, a tire blow-out) will flow the higher pressure quickly.
Today, electronic sensor technology exists such that pressure and flow can be changed dynamically, in a close-looped microprocessor-based system. A simple example is today’s service station tire pump. Program your desired tire pressure and the pump shuts off when it senses 36 pounds of tire pressure.
Flow Control Valves
All valves control flow. The industry term Flow Control Valve refers to its ability to vary the flow of a fixed pressure to its output side. There are manually controlled and current (amperage) controlled valve types.
Manual Flow Control Valves usually have a knurled adjustment knob or throttle. Once the desired flow is set, these valves remain in that flow setting until further adjusted.
Flow control valves operated by current are commonly referred to as proportional valves. As amperage is applied or varied to its solenoid operator, the output flow of the valve varies accordingly.
The primary advantage of these “proportional valves” is their ability to be used with a microprocessor-based programmable controller, particularly in closed-loop systems. In these systems, downstream sensors continuously provide feedback to the controller to change (or not) the current to the valve’s solenoid operator.
Other names for flow control valves include needle valves, proportional valves, and meter out valves.
Pressure Control Valves
Pressure Control Valves are commonly called pressure regulators and come in manual and electronic models, similar to flow control valves. Pressure regulators are designed to respond and maintain a controlled downstream pressure setting when a pressure loss or surge occurs. Each pressure regulator has a restriction, load and reference element to respond to pressure and maintain the desired output.
They are only used in closed-loop systems since they require downstream feedback to maintain a set pressure. Pressure Regulators are offered with either piston or diaphragm type valves. Piston types are better suited to rugged applications that require some accuracy and durability, while diaphragms provide precision control.