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Pumps Don't Build Pressure

hydraulics

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21 replies to this topic

#1 Toolpartzman OFFLINE  

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Posted October 07, 2012 - 06:05 AM

Its my hope that some day, we can finally leave behind the incorrect and confusing phrase "pump is building pressure". !!

NO FLUID pump, since the Romans moved water with a goat bladder has a pump built pressure! PERIOD. No fixed or variable displacement gear, vane, axial or radial piston EVER was designed or built to BUILD PRESSURE. Whether you're pumping peanut butter, hydraulic fluid, a mixture of chicken blood/fat, or water to a jet at 40,000 PSI. I've done them all and not one "built pressure".

PUMPS move fluid, period. They have various capability to move this fluid against different conditions and amounts of RESISTANCE, that we read as pressure on a pressure gauge. PRESSURE is a measure of RESISTANCE to PUMP FLOW, NOTHING ELSE.

When we read pump specs., say 10 GPM at 2500 PSI, the manufacturer is saying that the pump will MOVE 10GPM of a certain viscosity and temp fluid at a known speed against a resistance of measured 2500psi.

In my 30 years, the biggest hurdle in troubleshooting comes from somebody injecting " pump won't build pressure" into the conversation. They might wear out, and fail to move fluid, but that pump didn't "build pressure" when it was brand new. Sorry, guess this was a rant!

Edited by Toolpartzman, October 07, 2012 - 06:19 AM.

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#2 Michiganmobileman OFFLINE  

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Posted October 07, 2012 - 06:18 AM

....... Sorry, guess this was a rant!

Maybe so, but an informative rant none the less.
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#3 KennyP OFFLINE  

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Posted October 07, 2012 - 06:27 AM

That's nice info to know!
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#4 Toolpartzman OFFLINE  

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Posted October 07, 2012 - 06:35 AM

As a matter of fact, even in the most complex and sophisticated hydraulic motion control systems-THE PUMP IS THE ONLY component that doesn't "build pressure".

Now that I've calmed down a little--Its important that we use proper terminology because without it, it can cause others to improper, lengthy and expensive diagnosis.

Some 30 years ago, a customer called my office and ordered a $6000 -obsolete pump for a press that had been in service over 40 years. As I was on the way to see him anyway, I told my secretary to hold the order.
After looking at the machine, the fault was a $290 triplex relief valve, not the pump. That incorrect diagnosis might possibly cost the supervisor his job, because $6K would not have solved his problem.

So, when we teach folks its always better to keep with clarity and fact when it disagrees with common terminology.

Edited by Toolpartzman, October 07, 2012 - 06:53 AM.


#5 Gary400 OFFLINE  

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Posted October 07, 2012 - 06:48 AM

i know mine isn't
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#6 IamSherwood OFFLINE  

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Posted October 07, 2012 - 07:24 AM

So, the correct way to say that I think the pump is broken, would be...?

"I think our pump isn't moving enough volume of oil." ?
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#7 Toolpartzman OFFLINE  

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Posted October 07, 2012 - 08:11 AM

So, the correct way to say that I think the pump is broken, would be...?

"I think our pump isn't moving enough volume of oil." ?

Well yes Will, that's correct in that a pumps job is moving fluid and if a pump fails or is failing, the evidence of is is downstream at an actuator-cylinder or hydraulic motor etc. Nearly all our hydraulic applications involve transferring pump flow to a mechanical motion of some sort-when that motion changes it indicates a flow issue somewhere-bypass or leakage at control valving or the pump slipping as well- but the term "pump building pressure" is an improper diagnostic conclusion, because it doesn't do that. The phrase I always use is "system pressure" or the "pump is seeing x pressure. Lots of folks have rebuilt or replaced the most expensive component in the system , to find that didn't solve the problem.

#8 Toolpartzman OFFLINE  

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Posted October 07, 2012 - 09:03 AM

I guess its a personal issue simply because flow and pressure are carelessly used interchangeably. Its common. In 30 years of hydraulic diagnostics I bet I've heard "pump ain't building pressure" tens of thousands of times and raises my hackles. Is the damn cylinder lifting the load OR NOT? I've heard it from machine operators and not a gauge on the machine. I would think that a pump being the culprit is less than 20% of the time. Excepting for vane pumps, a pump will tell you whether its unhappy-sound, actuator motion or something, but nearly always the culprit is in an actuator seal or control valve seal. Pumps usually die a slow death and not abruptly.

#9 skyrydr2 OFFLINE  

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Posted October 07, 2012 - 09:14 AM

Not them JD piston pumps ;) ..... lol
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#10 Alc ONLINE  

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Posted October 07, 2012 - 10:32 AM

You right but I guess we'll always say things like " the pump not building pressure " instead of "we'er not developing the correct system pressure" So those that don't know the correct way the hyd system they are working on might get confused and misdiagnose their problem , thanks for the posts . hope it saves someone some day , Al
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#11 IamSherwood OFFLINE  

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Posted October 07, 2012 - 07:44 PM

Is the damn cylinder lifting the load OR NOT? I've heard it from machine operators and not a gauge on the machine.


I've been around hydraulics my whole life. As a kid, and through the school years, I worked for dad, at his machine shop.
He also built and sold Hydraulic and pneumatic cylinders and valves.
Alot of our equipment has hydraulics on it, and some of it is self made. The one thing I've learned, (the hard way) over the
years, is to take the time, and spend the money, and put "T" fittings in the system . Plug them, and if you ever need to diagnose
a problem, you can easily plumb in a pressure gauge.

The example, that comes to mind, was about 10 years ago, I thought the pump on the wood splitter, wasn't producing pressure, so
I drove 2hrs each way for a new one. Next day I went for a valve. On the third day, I picked up a new cylinder, and some "T"
fittings and a gauge.
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#12 dstaggs OFFLINE  

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Posted October 07, 2012 - 08:04 PM

Dang that is one of the Greatest thing about GTtalk read and learn from the Best. Thanks Lee the Rant gave me a lesson in something I didn.t know.

Edited by dstaggs, October 07, 2012 - 08:06 PM.

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#13 olcowhand ONLINE  

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Posted October 07, 2012 - 08:07 PM

Well Lee, when a hose bursts, it feels like pressure to me! And I have no resistance to it at all...I get the heck out of it's way! :smilewink:
But I do understand what you're saying.
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#14 IamSherwood OFFLINE  

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Posted October 07, 2012 - 08:27 PM

Well Lee, when a hose bursts, it feels like pressure to me!


No, it's, declining resistance.
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#15 UncleWillie ONLINE  

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Posted October 07, 2012 - 08:36 PM

I want to see peanut butter pumped at 40,000 PSI. I will bring a large loaf of bread
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