Is showing transducer blocks on P&ID control valves an optional requirement?
Is showing transducer blocks on P&ID control valves an optional requirement?
(OP)
I've done more than my fair share of FEEDs and Detailed Design and its something that I've never quite got an answer to.
I'm talking about specifically showing the control block (usually) showing the current to pneumatic line to a control valve.
Some projects do show it, some don't. Some don't even show it on the Legend sheet detail.
Anyone got a position on this?
I guess its often omitted as it usually comes with the valve.
I'm talking about specifically showing the control block (usually) showing the current to pneumatic line to a control valve.
Some projects do show it, some don't. Some don't even show it on the Legend sheet detail.
Anyone got a position on this?
I guess its often omitted as it usually comes with the valve.
RE: Is showing transducer blocks on P&ID control valves an optional requirement?
RE: Is showing transducer blocks on P&ID control valves an optional requirement?
It comes down to whatever serves understanding, visual clarity, and consistency. FWIW I personally lean towards showing the symbol because I like establishing a clear visual distinction between modulating and on/off actuated valves.
RE: Is showing transducer blocks on P&ID control valves an optional requirement?
RE: Is showing transducer blocks on P&ID control valves an optional requirement?
In general:
- if all CVs in this unit are fed with air then what is the reason to show this on P&ID? Distinction is reasonable only when a unit has different types of CVs
- if some CVs are fed with air, while other CVs with lets say oil then there is a reason to distinguish those to better understand which will fail during air pressure drop
Note that in the past a practice was widely spread to control CVs with impulse air, not 4-20 mA, because logic controllers were expensive and overcomplicated. So in the past a sound reason existed to distinguish I and P impulses and therefore how a particular CV is fed and how is controlled.
Note that at this time many units still have different feed sources at one time and place, e.g. as per my practice neighboring CVs may be fed with natural gas, inert gas and instrument air. In such case these details are critical for designers and operating personnel.
Note that some CVs (mainly depressurizing valves, shut-down valves, emergency emptying valves) have a built-in buffer and check valve intended for emergency supplying of gas during total pneumo failure. In this case it is critical to distinguish which CVs have extra safety devices.
Note that many processes may require some CVs to be fed with high pressure gas while the rest with common (low) pressure.