ID of P&ID symbols 1

[bimr]

Does anyone know what the symbols "I/I", "KC", and "UA" and "LY" are on this P&ID? The legend doesn't call them out. This is pump station with 3 VFD pumps.

 

[Snickster]

I think they are as follows but its been a while since I looked at a P&ID:

LY is a relay in this case it is an I/I (Instrument Air to Instrument Air - note that the 3-hash lines are pnuematic piping symbol) which takes a pneumatic signal from LIT as an input and converts it to an pnuematic output control signal to operate a device based on the functioning of the relay. In this case it looks like it is trying to control level in the pump station by what appeares to be a bubbling arrangement that creates a pressure in the sensing tubing based on level in the tank which provides input signal to LIT (level indicating controller/tranmitter) which sends a signal to the LY. The output of the LY is input to the VFD to automatically control the speed of the pump. The SC is a speed controller to manually control the speed of the pump and the hand switch HS allows control either manually or automatically. UA are just status lights that show if the pump is on or off.

 

[bimr]

The three hash lines are actually 4-20 ma signals. The three hash with the cross through is a 110 volt on/off signal. The two hash lines are pneumatic.

 

[georgeverghese]

I/I - current signal input / current signal output
KC - controller - unspecified parameter; maybe a sequence controller
UA - unit alarm
LY - level signal modifier ( usually some simple mathematical modifier acting on the input signal - may have one or more modified outputs)

 

[bimr]

Thanks George

 

[LittleInch]

The ISA version seems to go as
I/I - as above
KC - Time or schedule Control, so sequence controller looks like a good shout
UA - Multi variable Alarm. So could be anything.
LY - Level Auxiliary Device

But then I'd never seen three crosses on a line meaning 4-20mA ( usually a dashed line) and not with an extra line through it meaning 110V digital signal...

So it looks like a special set of symbols and it's not the easiest of P&IDs to follow without some sort of process and control description or a whole bunch of notes...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

LI, thanks for posting and agree with your comments.

 

[georgeverghese]

Many of the details behind these controls would be found in the process control narratives and the cause and effects diagram also - in older plants, these crucial documents are often missing, corrupted or worse still, non existent or considered privileged information.