Positioners are used to control the air load pressure on the valve actuators. The positioner forces the actuator to move the valve until the desired position is reached and balanced according to the output signal from the controller. The control signal to the positioner could be electrical or pneumatic. They can be 3-15psi, 4-20 mA, 0-10V, digital or different protocols like HART or Profibus.
Need help to select the optimal positioner for your valve and application? Please contact us or schedule a meeting with one of our product specialists.
Why use positioners
The main purpose of a positioner is to enhance the control resolution of the valve. They ensure the valve position gets as close as possible to the commanded position by the control system. They can mitigate the effect of dynamic variations that cause adverse controllability, such as changes in packing friction arising from corrosion, dirt, lubrication, sloppy linkage (causing dead band) and non-linearities in the valve actuators. They can also improve the response speed based on the received signal enabling faster air loading and venting.
How positioners work
Depending on the type of valve, positioners are normally mounted either on the side-yoke for linear valves or at the top of the rotary valves body. However, there is always a mechanical linkage to the valve stem. When the process variable (e.g. flowrate, temperature, pressure) differs from the set point, a control signal from the controller inputs the positioner. The positioner sends a corresponding air pressure load to the actuator. Once the valve position is altered and sensed by the mechanical linkage, the feedback signal is sent to the controller and compared to the set point to make sure that the valve has reached the desired position. No position feedback could be achieved without a positioner in the control loop, resulting in less control precision.
Positioners paired with different types of actuators
Depending on the actuation configurations, positioners can fit both double acting and single acting (spring return) actuators. Positioners for single acting actuators have only one air outlet to the actuator while double acting types have two air outlets to be used with actuators without spring.
Our different positioners
Ramén Valves offers a number of analog and digital valve positioners from Flowserve, Siemens and Schneider Electric. Some of them are presented below. If you want more information, please contact us or book a meeting with one of our product specialists.
Positioner PMV D3 from Flowserve
PMV D3 positioner, supplied by Flowserve, is the most intelligent digital positioners among PMV D-series; however, it is extremely easy to use. This type of positioner can be locally adjusted to fit both single and double acting pneumatic actuators. D3 type features a zero-bleed pneumatic relay reducing the air consumption which results in less operational (electricity) cost.
The PMV D3 series can offer wireless communication lowering the amount of wiring while eliminating wire damaging and preventing connectors from corrosion in the plant. D3 wireless utilizes dual backbone routers to deliver extra radio paths as a safety feature and can be configured by the user when the signal or power is lost. D3 model has different versions for explosion proof, fail freeze, intrinsically safe, remote mounted and version for SIL2 requirements.
Positioner PMV D20 from Flowserve
PMV D20 is a compact, robust, and intelligent digital positioner supplied by Flowserve, offering high control resolution (even on small valves). With simple design and easy operation this positioner is a proper choice for single acting actuators. It is also available in standard and explosion-proof housing for hazardous areas.
The PMV D20 series can calibrate itself automatically by pressing a bottom in just a few seconds. Its modular design also provides various options fitting different requirements.
All PMV D-series can offer ValveSight DTM predictive diagnostics system. This system enables a communication dashboard between operator and the valve. It helps operators to know the valve status and shows unexpected trends to avoid sudden plant stoppages.
Positioner PMV P5/EP5 from Flowserve
The PMV P5 and EP5 series are pneumatic and electro-pneumatic analog positioners supplied by Flowserve. These types of PMV series, with a modular and robust design, allow easy installation of I/P converter and/or feedback units and can provide high gain, long lasting and accurate performance. They can be supplied in various types proper for explosion proof, fail freeze and fail-safe requirements. Perfectly fit both single and double acting pneumatic actuators.
Positioner SRD998 from the Foxboro series by Schneider Electric
The Foxboro SRD998 series is a smart and highly reliable digital positioner supplied by Schneider Electric. Designed for both single and double acting actuators, SRD998 can be operated from control systems, controllers, and PC-based configurations.
The SRD series functions applying nozzle and flapper mechanism. This principle is all about a pressure signal produced by a mechanical movement. That is a fluid flow restriction through a nozzle covered by a flat plate called flapper generates the pressure signal.
Positioner SIPART P32 from Siemens
The SIPART PS2 electropneumatic positioner, a Siemens product, is a safe and reliable positioner series for a broad range of applications. They are suitable for both single and double acting pneumatic actuators. SIPART PS2 positioners have compact and modular designs with versions for remote position detection and remote-control electronics. These installation versions enable the use of positioner in critical circumstances such as severe vibration, extreme temperatures, water influences, applications where valve is hard to access and radiation exposure.
If you want more information about our positioners, please contact us or schedule a meeting.