Pump run status: Diaphragm pump:

I have a need for a DCS or PLC input: "XL" RUN STATUS from an air operated diaphragm pump. This is to verify operation of the pump. The pump is air operated from a Solenoid which is a DO from the DCS or PLC. I could easily put a limit switch on the solenoid for a DI to tell the DCS air to the pump is on, but this doesn't necessarily tell me the pump is running. Does anyone have a suggestion as to how I could prove the pump is operating - some sort of run status?

A pressure switch in the line from the solenoid valve to the pump.
Better yet use a flow meter or a flow switch.

Scott180zip,

I had a similar problem a while ago. This not the best solution. but it works for me.

I monitor the pressure side of the pump with a simple pressure switch. But what makes this system work for me is that I already had an air actuated ball valve on the output side of the pump also. So periodically the PLC shuts the ball valve and looks for the pressure switch to be made. The pressure setting on the switch is set high enough so that when the pumps is not deadheaded the switch is not made.

So my scenario is
1. Pressure switch made but ball valve open = blocked line
2. Pressure switch not made ball valve open, need to test system by shutting ball valve. If the pressure switch is made when this happens I know the pump is working.
3. If the test is done and the switch never gets made then I know the pump is not working.

You may not have the low pressure on the output side of the pump to make this feasible.

We had diaphragm pumps with two diaphragms and a back and forth action. We put a limit switch on them that should change states within a couple of seconds to ensure that the pumps were actually moving back and forth and not locked up. This was for a heavy thick fluid that we could not easily install pressure switches.

Or perhaps an flow switch on the discharge side of the pump?

milldrone said:

So periodically the PLC shuts the ball valve and looks for the pressure switch to be made.

Click to expand...

Just a word of warning for others who may read this thread and thinks about closing the outlet side of a diaphragm pump !!

Don't do it on anything other than an air-operated diaphragm

Mechanically-driven diaphragm pumps are "positive-displacement" meaning that there has to be somewhere for the material in the reducing cavity to go, and if that is closed off, something will "give" (i.e. Break).

Best practise for any P.D. pump application is to have a pressure-relief device, from outlet back to input, in the event the outlet piping is closed-off.

It is also common to put an accumulator bottle on the outlet of a diaphragm pump to smooth out the pulsation of the flow, especially on blending applications. If that is the case, the pressure switch idea probably won't work.

I would go for detection of flow in the outlet. I have in the past used a small and simple "vane" flow detection device. This had a rotor with a magnet in, and a reed switch or hall-effect sensor to detect rotation of the vane wheel. A small bleed flow (using 6mm poly line) was taken from the main flow, through the flow sensor, then back into the main flow. Each stroke of the diaphragm pump would cause the vane sensor to rotate, and I could easily detect the pulses with the PLC.

OkiePC said:

We put a limit switch on them that should change states within a couple of seconds ....

Click to expand...

Detecting the diaphragm movement does not indicate the pump is actually pumping anything.

on most a.d. pumps i've needed to verify pumping on we have installed magnetic stroke counters. you can buy the pumps with them or buy kits and retrofit your pump. this will only verify that the pump is operating and not necessarily moving any product.

I believe we are all sharing our past experiences with air powered diaphragm pumps. The responses all appear to be correct within each individuals experience. My guess would be that there is not a single sensor or solution that will work in every case, due to the variety of applications. The original poster has not given enough details for an answer that will work in his application.

FLow switch with dry aux contacts is the way to go...

In most cases, we have level transmitters in tanks with the pump (and valves) between. So we look at the change of level in both tanks to make sure that the pump is doing it's thing. We don't use flow or pressure switches nor do we put a position switch on the solenoid valve that supplies air to the pump.

we have certain valves on site that have no position feedback but we just use the solenoid feedback instead which would even give feedback if the air has failed.
I would go for outlet flow switch on the process side as a guarantee that the pump is running, also this could highlight problems if the pump fails, past experience with these pumps is that if they get airlocked then they race high, hope this helps.