I'm not a controls engineer, and my company doesn't have one on staff, so I need some help. I have a scenario where I have a pump connected to a pump suction tank. The tank has 4 float switches installed. One switch is LSL which turns the pump off on low level. The next switch is LSH which turns the pump on on high level. The third is LSH which turns on an indicator light on a pump panel. The last switch is a LSHH which turns on an indicator light on a pump panel and also sends a signal to an autodialer. We currently show the LSL and LSH that turns the pump on or off with an LSL bubble that has a dashed line going to one side of the motor with the word "OFF" and an LSH bubble that has a dashed line going to other side of the motor with the word "ON". My manager thinks that this is not the correct way to show this. My manager's point is how can we have a LSH that turns the pump on, and another LSH that illuminates a light indicating a possible problem. He thinks that we should show a LSH that turns the pump on, a LSHH that illuminates the light and a LSHHH that illuminates the light and dials the autodialer. I told him that I didn't think there was such a thing as an LSHHH bubble on a P&ID. Can someone help with what is the correct way to show this on a P&ID?

Thank You

 

We often use xxHHH in the petrochemical industry where we have regular DCS trips and Emergency Shut-Down System trips. Usually we reserve the HHH & LLL for the ESD trips.

If there's not room in the bubble you could put the LA inside and HHH outside the bubble.

If it's a multi-purpose light it might just be designated UA with a different tag No.

There's no hard and fast rules as far as P&IDs go. you can do what you like, although I think most base their drawings on ISA guidelines. No-one told us to do it this way, we just made our own rules and they change from job to job.

If it gets too complicated, cover it with a note on the drawing or a separate document.

Hope this helps.

 

Revision,

Another way around the problem is have a separate tag for the pump, often given the pump No LSH & LSL with no associated alarms.

Then have a separate tag for the tank (these are the alarms) LSH/LAH and LSHH/LAHH.