level switch vs pressure switch

Charbel · Jul 25, 2014

Dear,

For protecting the pump against dry running, it is better to use low level switch in the tank or pressure switch on the suction side?

I tend to go for low level switch in the tank to protect the pump from dry run, please advise of any thought.

thank you!

charbel

nonuke · Jul 25, 2014

Why not use a flow switch after the pump of the type: IFM - SI5000

John Soltesz · Jul 25, 2014

Another way is to monitor the pump inlet line with a point sensor switch. If there is liquid then OK to pump.
Look at the E +H Liquiphant FTL20 types of sensors.

Mickey · Jul 25, 2014

I don't think one can say which is better. But I would go with the level switch.

Most tanks will have a low and high for control and a Low-low and High-High for protection. The extra switches provide extra protection if the low does not shut the pump off the low-low will.

Then again a pressure switch closed to the pump would protect against closed or pinched valves.

Your installation will dictate. Maybe you need both.

Tom Jenkins · Jul 25, 2014

For protection against running dry the level switch, regardless of type, is probably the better bet. A low pressure (high suction) switch on the suction side of the pump would be used to protect against cavitation. If you have a flooded suction pump with normal piping that is probably not a problem.

TConnolly · Jul 25, 2014

Level switch is the simplest.

There is however another option to consider if level switch installation is challenging. www.loadcontrols.com has a sensor where you place a CT around a motor lead wire and it can detect pump dry run. It also works if someone closes the pump suction valve.

nonuke · Jul 25, 2014

If you use a level switch, you probably also need a pressure switch because you might have a closed valve after the pump (liquid but no flow). If you use a flow switch you don´t need any other switch.

Charbel · Dec 12, 2014

Dear,

I assume a flow switch will needs to be located after the pump, because a flap type flow switch before the pump will not make a difference but on the contrary it will stop the pump from running because the pump will need to run to make flow and to make the flow switch work.
I might use a thermal based switch on the discharge but am i not being too late to stop the pump?, the thermal based switch will have to detect no flow in order to stop the pump which is too late?

I think the best would be pressure switch on suction combined with low level switch on the upstream tank

Any thought about this?

Thank you!

charbel

realolman · Dec 12, 2014

I don't think I'd bother with the pressure switch at all

I think it would be more trouble than it would be worth

The flow switch can be a pain as well, and you will have to ignore it till you get the pump started

use floats

Rumiat · Dec 12, 2014

Well it all depends on your system actually.

If you have a foot valve installed (assuming tank is lower than pump) that would make sure your pump remains primed, just go for a low level switch.

If you choose to use a flow switch, I think you may have to bypass the flow safety system during pump starting and adjusting its suction/discharge valves. So low level is a good option I would say.

Hope this helps.

nonuke · Dec 12, 2014

I also use a level limit switch model Liquiphant FTL20 (vibrating forks type) before the pump. If pipe empty, the pump won't run. Works all the time.

level switch vs pressure switch

Charbel

Member

nonuke

Member

John Soltesz

Member

Mickey

Lifetime Supporting Member

Tom Jenkins

Lifetime Supporting Member

TConnolly

Lifetime Supporting Member

nonuke

Member

Charbel

Member

realolman

Member

Rumiat

Member

nonuke

Member

Similar Topics