Interested to Buy Any Domain ? << Click Here >> for more details...
why we use double acting valve and where?
- 1 Answers
- 10168 Views
- Aker Solutions, I also Faced
- E-Mail Answers
Answer Posted / sam
Normally a control valve is refer to by it's fail position.
This means "what position will the valve move to should the
supply air or control signal to the valve falls away". This
is important to safe guard the process at various places so
some valves will be fail open and some fail close. In order
to have valve as a fail open or close the valve the actuator
have to be spring loaded. So by having the spring on top or
bottom of the actuator piston, will determine if it will be
a FO or FC valve. This kind of valve is also called single
action since it will only have one output from its
positioner to either the top or bottom of the actuator. The
positioner on the valve is also setup as a single acting
positioner since it will only give a single action to the
actuator, the reverse action will be done by the spring. The
problem with this setup is that it is possible that the
process might be so strong or the pressure so high (during a
blow down or ESD shutdown in the plant) that the spring
might in certain instances be to week to push the valve into
the fail position quick enough, due to the back pressure
from the process and can cause damage to the plant or even a
explosion. To make sure that the valve will go to the fail
position we install a double action positioner with two
outputs. One goes to the top of the actuator and one to the
bottom. This is also very helpful to do very accurate and
stable control on a high flow line since the pressure from
the position do the actual control and not spring control
one way and positioner control the other way as in single
acting control valves. It is also solving the problem that
the valve will now be forced into the fail position by the
spring as well as the positioner supply pressure during a
emergency.
In shutdown valves (open/close ESDV's) the same is true and
sometime at critical and high pressure points we use
hydraulics instead of pneumatics as the double acting agent
to make sure the valve will close during a emergency.
So to summarize the double acting action in ESD and control
valve is just there to make sure the valve will do what it
was designed for. Call it a extra fail safe if you want. In
theory not needed since a single acting valve should do the
trick just as well,but in practice you are at time very glad
you did it especially if you look at the kind of pressures
the valves are working on. With those kind of flows and
pressures you don't want to leave anything to chance.
| Is This Answer Correct ? | 29 Yes | 1 No |
Post New Answer View All Answers
How to change dcs card in online. (Dsc is maxdna)
pls suggest suitable MOC of diaphragm for pressure measurement of UREA grade solution service fluid.
please tell me what is a light up procedure of Cfbc boiler and what it's axuillaries of cfbc boiler?
Please any one can provide latest aptitude test,technical test and interview questions for tata consulting engineering (TCE) i need it asap thanks in advance
How is PH sensor works ?
what is a vortex flow meter,mass flow meter and electromagnetic flow meter.particular use of this.means in which condition particular meter is used.
how to tune siemens sipart electro pneumatic positioner..plz tel me..
Displace type LT to be calibrated in workshop, wt. 40, dia- 60 mm, density- 0.8kg/cm3.
1. For Steam drum level signal, why do we compensate with drum pressure signal? 2.For main steam Flow signal is comensated with main steam temperature signal and main steam pressure signal why?
all types of liquid analyzer principle with drawing?
How hart protocol can be connected with control valves?
I have a Control VAlve having size of 2 ".Only the known parameter is Pressure drop . Its 2 Kg. Then How to calculate control valve sizing means Cv.
Hello to all....I am an Instrumentation Graduate and i am passed out in this year only.. I am unable to find the job in my core instrumentation.. so any boby tell me how to and where to search the job....please...and also tell me i there are any courses offered in the instrumentation stream so i can do it... you can send your suggestions to my mail-id i.e Ganesh20084u@gmail.com ... please..
can anyone can let me know in Eurotron Micro cal 2+ calibrator in milli amps source mode we are not able to get 20 milli amps output it only produces 1.52 milli amps out, but display shows increase in milli amps , and err6 displays, let me know how to remove the err 6.
why we r opening HOT BYPASS valve during startup of a compressor?
