Answer / carl_ellis

Pneumatic positioners equipped with a bypass option can be removed for maintenance without interrupting the valve service.

A position bypass is/was a common optional feature on pneumatic positioners that receive a pneumatic control signal (typically 3-15 psi, 20-100 kPa, or 0.2 - 1.0 bar) from a controller or I/P.

The bypass option is a pneumatic switch. The inlet is the control signal. The valve's outlet is either the positioner (normal mode) or the actuator (bypass mode).

If the positioner needs servicing, the bypass switch is changed from normal mode to bypass mode and the control signal will drive the valve actuator directly. The bypass assembly can typically be removed from the positioner with a couple bolts so that the bypass assembly remains connected to the process, while the positioner is removed for service.

Positioner Bypass operation does not work
- on valves with actuators whose input signal range does not match control signal range (a 1:1 output:input signal ratio). A valve actuator that requires 40-60 psi to actuate will not be actuated by a 3-15psi control signal.
- for split range valves
- for valves with control action (direct or reverse) the opposite of the control signal action.
- Electropneumatic positioners that use a 4-20mA input signal have no bypass option because there's no pneumatic signal to bypass to the actuator.

Carl Ellis
Measure First

Can anyone convert a 5/2 way or 3/2 way valve into an ISO valve?

0 Answers  

---

What is TMR

3 Answers  

---

how to overhaul control valves.what are the proper procedures.

1 Answers   Jindal, QAFCO,

---

how many types of elements are there?

1 Answers  

---

when the instrument tapping on pipe line is located below and transmitter is located above the tapping point for liquid service transmitter, what should we do, is there any additional drain valve is required??

0 Answers  

---

---

if conical type tank in top LEFT side solid material coming but LT MOUNTED IN TOP OF LEFT SIDE, how to measure ultrasonic level transmitter ?

1 Answers   Cairn,

---

generally transmitter power supply having some range(12v to 35v) but the out put(4-20 mA) must same for given input.If we vary the power supply voltage then output mA also to be change according to V=IR. Is there any voltage regulator in the transmitter ?

1 Answers   Indian Steel,

---

why we use negative 24vdc to a proximeter

4 Answers   KNPC,

---

what is the difference between profibus and controlnet networking.

0 Answers   HZL,

---

Give me best instrumentation Books name..Ple...

6 Answers  

---

what is difference between wheatstone bridge, pirani gauge and strain gauge ??? explain its principle and working

4 Answers  

---

What is the difference between working pressure and calibration pressure of a control valve

0 Answers  

---