Internal gear Positive displacement Pump ( Harmful high Diff P and construction) 1

[bmw318be]

1Would too high differential pressure could damage the internal gear pd pump componenta range around 10 bars above ?
Rotor, idler, bushing and so on

2.As some of commons types of pump casing construction are
Cast iron, steel, stainless steel, carbon steel:

How to determine the suitability of material compitability of different types of fluid ? I hope anyone with commons liquid types are able to share their casing's material application

 

[DubMac]

Do not be afraid to ask the pump manufacturers; most of them do not bite.

 

[bimr]

You can instantly ruin a gear pump if the pump is operating at too high of a pressure.

An important requirement for gear pump systems is to include a pressure relief valve in the discharge piping (fairly close to the pump itself) to relieve pressure back to the storage tank or other liquid supply source, when downstream valves are shut off. Some gear pumps include a built-in pressure relief valve which will provide the same critical pressure relief but only for very short time periods. This is because the built-in pressure relief valves are internal to the gear pump and simply recirculate the liquid inside the gear pump itself. Recirculation inside the gear pump for other than very short time periods will cause the liquid to build heat quickly and will eventually ruin seals, packings or other key gear pump components.

 

[bmw318be]

How high is high ? . Are the pressure that damage the internal gear pump is the pressure developed by the pump which is the differential pressure ( discharge - suction pressure)

My doubts in PD pumps :

How the suction pressure is developed and sometimes we are getting - (negative) suction pressure. How suction pressure usually is calculated

On the contrary of suction pressure, discharge pressure is usually determined by process, how the process able to determined this on the design stage of their system.


If the discharge pipe is very long 1 to 2 km and 4 inch pipe, does this determined the discharge prrssure required or the diff pressure

 

[bimr]

The pump manufacturer will set the design pressure of the pump.

A positive displacement pump moves a set volume of liquid. Pressure is created as the liquid is forced through the pump discharge into the system. The pump converts energy into pressure. Positive-displacement pump create flow and discharge pressure is created by system's response to flow (ie: discharge pressure = discharge line total backpressure at pump outlet flange).

Note that a rotary unit will continue to pump if there’s a downstream blockage. So, rotary systems require some type of safety pressure-relief valve at or immediately downstream of the pump to protect against over-pressure. It doesn't matter what the discharge pressure is; the pump is going to transfer that volume regardless, i.e. "positive displacement". If discharge valve is closed, then either the motor will shut down or something will go Kablooey.

 

[bmw318be]

So in internal gear pump we cant afford to have
Blockage on the discharge. So most of over pressure basicly due to blockage ? Isnt that if we running the motor at higher speed, the pressure would increase ?

Would we able to throttle the discharge valve to calibrate the discharge pressure in pd pump, so small opening would we get higher discharge pressure. i wonder how we could simulate the flow and discharge by using throttling methods

 

[bimr]

It would preferable and simple to adjust the speed of the gear pump than to attempt to throttle the discharge

 

[bmw318be]

Any idea if I could test perform the pump by using the discharge valve, for example: at 400 rpm my pump curve should get 20 m3/ hr @ 5 bar and i am having discharge valve. Should I throtlle to reach 5 bar and measure the flow should be approx 20 m3 / hr.

 

[Pumpsonly]

The pump curve is based on differential pressure..so you must measure the suction pressure also.

 

[bmw318be]

Thx so the suction got to be throttled by small amount to get the rated diff pressure,

 

[hydtools]

What is the pressure for which the pump is rated? 10 bar is not a very high pressure.

Do not throttle the suction. Adjust the discharge pressure with a valve to be 5 bar above whatever the suction pressure is if you want to create a 5-bar differential across the pump.

Ted

 

[bmw318be]

Actually pump is rated at around 2 bars, however o want to perfprm test the pump to design pressure of 12 bar differential at rated speed, viscosity and flow. Anyone know if it is advisable for me to throttle to achieve rated diff pressure ?

I would like to know fpr hydrostatic test, it is advisable to hydro pressure test at max allowable working pressure of the pump and adding 50 % more assuming maximum is 25 bars and 32.5 bar run hydro test.

Curious if api 676 has this requirement ?

 

[bimr]

A hydrostatic test is typically accomplished with a separate pressurization pump.

The pressure is the system is raised to the hydrostatic test pressure, the pump is disconnected, and the pressure is then monitored for a set period of time.

 

[bmw318be]

Can you elaborate further how could it be seperated pressurization pump ?

 

[Pumpsonly]

the questions you are asking here are actually very fundamental and basic in pump. Instead of keep on asking , I would suggest you read up more literature's and articles in pumps.

 

[hydtools]

A simple hand-operated piston pump could be used to pressurize the system after the system is filled with liquid.

Ted

 

[bimr]

Search google for hydrotest. Here is a typical test procedure:

http://www.cityoffullerton.com/civicax/filebank/blobdload.aspx?blobid=3392

The system is filled with fluid and then the test uses a small pump to raise the pressure to the desired test pressure.

 

[bmw318be]

pumpsonly, this forum is to ask question and no one restrict not to ask fundamentals .

 

[Pumpsonly]

bmw381be

Question such as " Curious if api 676 has this requirement ?"

You are expecting other to feed you instead of trying to find out your self for such a simple matter.

 

[bmw318be]

The fundamental could be challanged if you are experience enough, I am not checking as I do not have an Api guide so I would just like to bring it if most test usually be conducted deviating from api requirements.