Air diaghragm pumps

[ake71]

We currently have a (3")air diaphragm pump running at 42m3/hr
We want to install a second air diapghram pump (total flow 80m3/hr), but after further investigation I found that I needed to put in a pulsation damper for each pump because I will now have 2 pumps in parrallel and may cause an inertial pressure spike.In addition a return valve is required for each line if botyh pumps are running because this will The suction is 5 to 8 meters and we currently have a priming pot(1000lts) prior to the diaphragm pump. I am not sure if a priming pot is required?
Also i was told that what ever the air pressure is will be the discharge fluid pressure-is this correct?

 

[moltenmetal]

An ordinary air operated double diaphragm pump will stall at a pressure less than the supplied air pressure. The maximum pressure it can generate under any circumstances is the supplied air pressure- at zero flow. But what its discharge pressure will be at any given flow is determined by the flow resistance of your system, not by the air pressure.

Note that there are some funky air diaphragm pump designs with linked diaphragms of different areas such that they can generate a stall pressure 2-4+ times as high as the supply air pressure.

 

[Latexman]

I've put two AOD pumps in parallel before and got nowhere near 2X the flow. They fight each other and the theory/math doesn't work that way, especially if the parallel sections where the pumps are are short compared to the single suction and discharge sections. And, they are not PD pumps. They have pump curves more like a centrifugal.

Good luck,
Latexman

 

[ake71]

Thanks for that but what about the pulsation dampers. Do I need them because I will be running two in parrellel?
Also do I need a proiming pot or will the AOD pumps hold suction, even when they are not running?

 

[micalbrch]

Yes, you will definitely need a pulsation dampener although it seems that your existing pump (42 m³/h) does not have one what is surprising to me.

Priming pot? Not sure but if the existing one needs it, two in parallel will need it by all means.

Keep in mind what Latexman wrote. He is right. You will never get twice the flow with two AODs running in parallel.

 

[Compositepro]

You have not supplied any particular reason why you would need a pulsation damper. Inertial pressure spikes are not a problem as they can be with mechanical reciprocating pumps. The pressure output of the pump is limited by the driving air pressure, which is probably why Latexman says they are not positive displacement.

However, they are PD pumps in that they displace a fixed amount per stroke. It is the air drive that behaves differently than a constant speed induction motor.

AODD pumps have inlet and outlet check valves so they cannot work in resistance to fluid inertia, except by drag.

A damper would probably allow you to achieve a higher overall flow rate.

 

[micalbrch]

The need of a pulsation dampener is determined by the stroke volume, the operating pressure and the kind of pump. An AOD works like a simplex double acting pump. A 42 m³/h pump has a rather big stroke volume. The only think we do not know is the pressure. But the other two facts lead me to the advice that a pulsation dampener is mandatory, especially when two of the units shall feed the same line.