Pressure & Flow - Reciprocating pneumatic piston pump - Help!

[WilboSwagons]

Hi Team,

I'm going to try and keep this as short as possible (solve one problem at a time).

I'm trying to choose a reciprocating pneumatic piston pump to suit my application -pumping automotive fluids from a storage tank to a hose reel & dispenser out of a metered dispenser.

The main thing i'm struggling with is the pump performance charts. I've read through this from Graco (Pages 26 & 27 of the PDF or 24 & 25 of the document) - Link

I don't understand why when the flow rate goes up while the outlet pressure required drops (it's the same with all the pump of the same type not jsut htis example)- I understand this may have something to do with boyles law, but I can't find anything that explains how to apply it do a dynamic system.

Another contribution to my confusion - When you compare it to double diaphragm pumps they are the opposite - Link. I would use one of these but the calculated pressure loss is too high in the system

Any links or help appreciated. Feel free to roast me if i'm missing something simple

 

[gruntguru]

The flow rates are SCFM which is air at STP. These air motors do not have internal expansion so the air consumption per stroke is essentially the swept volume of the motor piston but at the supply pressure. If the supply pressure is increased, the same stroke consumes the same volume at supply pressure but this equates to a greater volume of air at STP.

je suis charlie

 

[WilboSwagons]

Ahk, Excellent I get what you mean. I've been looking at it in the wrong order for what i'm trying to work out I think.

Now for part 2.

Is my thinking process correct?

Would I be correct in saying that one of the ways I could find the max flow is to use the SCFM & the air pressure (it can be regulator to suit specs) of the air compressor to give me my max fluid flow which I can use the performance chart to give me the fluid pressure?

If the above is correct do I then work out my pressure loss in the system and take that from the pump fluid pressure and as long as that is a positive number we'll get our max flow?

Or is there an extra step i need to do to work out actual flow taking into account the pressure loss?