Valves positioners are practical solutions to streamline your valve fluid system. Simply put, a positioner is a device that ensures the valve is at the correct operating position according to the controlled signal.
When changes are made to the fluid system, the valve needs to adapt to the new conditions. With a positioner installed, the valve will adjust to the correct position based on the mechanical feedback from the valve stem and controller.
Before we dive into valve positioners, it is important to understand that a positioner can only be used in combination with a valve actuator. A valve actuator is the mechanism that opens and closes a valve. Instead of manually operating your valve, an actuator can be installed to allow the valve to be adjusted remotely.
Actuators are power-operated and rely on pressure or electricity to rapidly operate valves. If you aren’t using valve actuators, check out these 5 Reasons to Install a Valve Actuator. For even more information, read our Quick and Dirty Guide to Valve Actuators.
REASONS TO INSTALL A VALVE POSITIONER:
- MINIMIZING FRICTION
Positioners minimize friction effects of valve stem packing and the resulting hysteresis. This is especially beneficial for high temperature packing materials like graphite.
- INCREASES USAGE OF 4-20 mA ELECTRONIC SIGNALS
I/Ps can be located in the positioner that is on the valve.
Positioners allow for fine control with better resolution and accuracy through full use of signal. This offsets the variation of the actuator’s range spring rate, which can vary ±8%.
- INCREASED RESPONSE TIME
Positioners increase the response time to a change in the process. This allows for faster loading and venting.
- NEGATES FLOW-INDUCED REACTIONS TO HIGHER PRESSURE DROPS
This compensates for internal force imbalances.
- INCREASED FLEXIBILITY
Permits use of piston actuators with high instrument air supply pressures.
- SELECTION OF ACTUATOR BENCHSET RANGES THAT AREN'T MATCHING
Positioners facilitate selection of actuator benchset ranges that aren’t “matching” or “multiple ratioing” from the signal. For example, using a 3-15 psig signal with a valve benchset of 10-35 psig signal. However, if the larger value of the benchset is above 15-18 psig, a positioner is technically required.
- ALLOWS FOR SPLIT-RANGING
This gives you the ability to use one controller for two valves; 4-12 mA and 12-20mA.
- CHARACTERIZATION CAMS
Positioners allow for incorporation of characterization cams to vary from the rotary control valve’s inherent character to a formed characteristic.
- SEATING FRICTION
Overcomes seating friction effects at travel below 10%, allowing throttling near the “closed” position in a rotary control valve.
Valve positioners are available in three different configurations; pneumatic, analog I/P, and smart or digital positioners. Any of these would be a great addition to your system(s). The automation of a valve positioner will increase your plant efficiency, saving time and money while reducing downtime.
Have a question about installing a valve positioner in your system? Ask us about it! We gladly provide technical assistance to businesses and municipalities in Wisconsin & Upper Michigan.