Pumping Hydraulic Fluid

[quarlest]

Can a typical AOD be used to pump hydraulic fluid (~100 cSt) with a suction line having the following: length of about 40 ft, an overall height increase of about 2 ft, and ~8 elbows? Can it draw that much suction? I don't assume it can, but what would you recommend for this? We want to bring the pump inside the building as opposed to being mounted on top of the oil tank outside, for various reasons. Thanks.

 

[JJPellin]

What is an AOD? I assume it is some configuration of pump. Any pump, even a positive displacement pump, has a certain amount of Net Positive Suction Head Required in order to pump without cavitation. The manufacturer may state it as NPSH(r) in feet or they may specify maximum suction lift (also in feet). If the supply tank is atmospheric, you have about 32 feet of NPSH(a) at the surface of the liquid in the tank due to atmospheric pressure. You need to calculate the flow losses through your suction piping. You then take the 32 feet of atmospheric head, subtract the flow loss and the elevation increase (you indicate about 2 feet). If the remaining head is at least 2 feet greater than the NPSH(r) specified by the pump manufacturer, you may be OK.
An example:

I have well pumps at both of my cabins. The first one is a shallow well pump that takes suction from the water table 24 feet below the pump. It can lift the fluid this far because it must have an NPSH(r) of 6 feet or less. The pump at the other cabin is pumping from an artesian well about 75 feet from the cabin. It takes suction through 75 feet of 1" hose with about a 2 foot elevation rise. It has more problems keeping suction than the other one. The flow loss in the long suction line is too great even though the elevation rise is much less.

Depending on the type of pump, priming could be a problem. You might need to put a check valve (foot valve) back at the tank so the suction line cannot drain back when the pump is shut down.


Johnny Pellin

 

[quarlest]

AOD is "air-operated diaphragm" pump.

 

[ClicketyClack]

I have seen AOD's collapse a tank with their suction abilities.

I personally would not recommend this setup. When a diaphragm pump pulls a high vacuum on the suction stroke the high vacuum will try to pull the diaphragm through the suction port of the pump. This will reduce the life of the diaphragm and possibly cause it to burst near the area of the suction port.

You need to calculate the NPSH available and run it by your AOD vendor.

 

[TenPenny]

A typical AOD (air operated diaphragm) can handle a 12-20 ft suction lift dry.

You'll need to look at your flow rate and friction, but I think it will be fine.

The main problem with AODs is the pulsations, and the noise of the air exhaust, so make sure noise won't be an issue when you put the pump inside.

 

[Artisi]

I agree with TenPenny that your AOD should be fine on this duty, however, my standard response is if you have a technical question on the capability of any pump - contact the manufacturer - who is better qualified than them to make recommendations.