Gear pump pressure

[qoo2345]

Hello,

i have a setup where i uses a small gear pump. It is a brushless pump with a inner controller. It is max 10 bar, max 1liter per min. The seller told me when it 0.1 Lpm it would be at around 7 bar. However when i regulate the flow with the controller, my pressure gauge doesnt show any pressure change however there is flow rate changes. I was wondering is this how gear pump works? Do i need to use a throttling valve to make the pressure go up? What do i need to make the liquid have around 7 bar pressure at downstream.

Thanks

 

[LittleInch]

Can you sketch your system so that we can see how it fits in. In general gear pumps are effectively constant flow pumps (i.e. once you set your variable speed device). What the vendor probaly menat ot say was that it could deleiver up to 7 bar, but this is wholly down to the system you are connected to. If there isn't 7 bar back presusre at that flow, the gear pump doesn't care - it just merrily pumps its 0.1l/min (or whatever you've set it to) at whatever backflow exists at that flow rate, be it virtually zero barg, 1 barg or whatever, up to a maximum of 7. If you dead head the pump or have a highe rback presusre the pump will eventually stop or stall once the pressure reaches a certain value where the motor can't turn it anymore - probaly more than 7 bar, but not a lot more.

So yes, if for whatever reaosn you want a higher presusre downstream of your pump at a given flow, then you need to raise the system pressure atrificially by means of a throttling valve or other device to restrict flow - e.g. an orifice plate or smaller diameter tubing.

My motto: Learn something new every day

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

 

[qoo2345]

So if i were to induce pressure, i.e a RO filter cartridge so i must put a throttling valve at the exit to make water pressure buildup inside for my required pressure? Cause i rarely worked before with rotary or reciprocating pumps, so i was not sure how to you operate them. So the main idea if you were to use positive displacement pumps, you would need a resistant for pressure build up?

 

[GaTechTheron]

You are correct. In the ideal case, the pump will deliver whatever pressure is required to maintain the flowrate. This is the basis of a positive displacement pump.

Note that as pressure builds, your motor will likely being to slow down, and fluid slip in the pump will increase, therefore you will see a dip in flow.

 

[LittleInch]

Yes, that's about the right approach. As gatech says as the pressure rises the flow will drop off a bit, but for pd pumps generally not more than 10 to 15%. You operate positive displacement pumps to give you a near constant flow within a large pressure range.

My motto: Learn something new every day

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