Diaphragm pumps & Flow-monitoring

[Subystud]

Hello -

I am wondering about the necessity to include a Flowmeter in a pump skid I am developing.

System:
Fluid at room temp., Pressure inlet = 10ft of suction head (varies), Discharges Pressure = 50psig, viscosity = 10-40cP.

Specific pump:
Grundfos DME 60-10. (60 Lph, 10bar max. discharge).

Dosing (i.e. knowing how much chemical) is important, for reporting and quality.

My understanding:
1. With proper calibration, Diaphragm pumps can be self-metering by monitoring the strokes.
2. Diaphragms wear out, and leak-by can occur, thus the need for regular calibration.
3. Discharge volume can vary with varying suction head (possibly related to Item 2)

My questions:
1. Would you always include a flowmeter for the above diaphragm pump application?

Also, the users of this equipment notoriously will not calibrate the pumps. Thus, I feel a flowmeter is the most immediate remedy for this issue. Atleast remotely I can compare dose-strokes to the flow meter.

Thanks -

 

[petrochemical87]

yes a flowmeter should be included in the discharge of the pump if the amount of chemical dosed is to be accurately calculated.

 

[micalbrch]

I assume you have a metering pump with manual stroke control? These pumps are rather precise. So, there is not automatically a need for a flow meter. If the suction lift (negative head) varies, the filling efficieny and thus the flow will vary. In this case a flowmeter is helpful. But if you have a postive head which varies, the filling will always be pretty constant. Diaphragms wear, that's correct. But these pumps usually have a rupture leakage detection device which shuts down the pump in case of a diaphram rupture.

 

[Subystud]

It is a positive head. 5500 gallon tank that's at 15' liquid level full. The tank gets drawn down to as low as 3' of head (~1000 gallons - irrelevant). The pump suction is about 1.5' off the ground. So, the head is positive and varies between these levels.

I believe a flowmeter will make it into my specification.

Thanks -

 

[LittleInch]

Slightly irrelevant point, but also include an actuated valve in the outlet so that you don't accidentally draw fluid through the unit in the event of vacuum / very low pressure in your injection pipe (might be very rare but it has happened...) whilst the pump is off.

For this type of application, your flowmeter probably should be a PD type device as well to avoid errors due to any pulsing flow.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way