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Circuit pressure

Circuit pressure

Circuit pressure

(OP)
Hi,

I'm facing the following problem: in the project, i've calculated the pressure drop along a closed circuit. The calculations gave me aprox. 3,5 mH2O of pressure drop. This was calculated for a optimal flow of 240 lt/h. After the installation was made, the max flow that the pump was able to provide was 120 lt/h. The first thing that i thought was that the circuit pressure loss was much greater than th one i've calculated in the project and therfor the pump was working in a lour point of the pump curve, so that it could overcome that loss.

After this i've started to think much deeper in this, and i've figured another reason, that i would like to see commented. In this circuit, the pressure vessel is installed after the pump. I wonder if the pressure is limited by the expansion vessel defined pressure, wich may not be enough to overcome the circuit pressure loss.

I would like to hear some comments about this.

Thanks!!

RE: Circuit pressure

Where is the vent to atmosphere?

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Circuit pressure

Carefull, you'll out think yourself.

The circuit head loss (flow resistance) is much higher than you've calculated.  That forces the pump back to the left side of the curve and lowers the flow.

 

"Make everything as simple as possible, but not simpler." - Albert Einstein (1879-1955)
***************
http://virtualpipeline.spaces.live.com/

RE: Circuit pressure

(OP)
MikeHalloran,

In the top of the circuit. But now it is closed, because the circuit was filled and removed all the air.

BigInch

Ok. That was my cnclusion. But what is the possible reason?

Thank you both!

RE: Circuit pressure

What product and temperture, diameters, lengths, elevations...
Do you have a schematic you can post?

"Make everything as simple as possible, but not simpler." - Albert Einstein (1879-1955)
***************
http://virtualpipeline.spaces.live.com/

RE: Circuit pressure

(OP)
BigInch,

It's quite complicate to draw now a schem, but i understand what is your point. You want to confirm if my calculations were correct.
Let's assume yes and if we don't find a reasonable reason, then we assume that was my failure.

Thanks

RE: Circuit pressure

I have no interest in your calculations.  Its just that is is quite difficult to make any helpful comment at all without adequate information and arrive at any other conclusion than what you have already drawn for yourself.  Until then, I'll have to agree.
 

"Make everything as simple as possible, but not simpler." - Albert Einstein (1879-1955)
***************
http://virtualpipeline.spaces.live.com/

RE: Circuit pressure

If your calculations are correct:

You are using the wrong pump.

The pump was incorrectly specified.

The wrong pump was delivered and does not meet specifications on the order.

If you could provide a schematic as Biginch requested he may see an error in connecting the pump.  Or an unaccounted for system resistance to flow resulting in low pump flow.

Ted

RE: Circuit pressure

Pump installed backwards.
Valve not fully open.
Vapor locked.
Welder's gloves left inside the pipe.
Dead armadillo.
 

"Make everything as simple as possible, but not simpler." - Albert Einstein (1879-1955)
***************
http://virtualpipeline.spaces.live.com/

RE: Circuit pressure

I saw a dead rat but never an armadillo.  

RE: Circuit pressure

They love to run into uncapped western hemisphere pipe ends at night.

I found one glove once, said "well now we'll have to wait for the other one and, sure enough, it turned up a few days later.  Also found a hard hat once, said the same thing, but fortunately the guy only had one head.

"Make everything as simple as possible, but not simpler." - Albert Einstein (1879-1955)
***************
http://virtualpipeline.spaces.live.com/

RE: Circuit pressure

Seen a dead dog, snakes and cane toads, plus the usual, gloves, welding rods and hats etc which is fairly normal on construction and plant sites. The dog caused a problem completely blocking the impeller eye, the snake (small)  got thru to the impleller on the house pressure pump - took a while to figure out the problem  - but cane toads are not a problem on 6" contractor pumps - just chops them up and spits them out.

For the OP.  Check the pump is running correct direction.  

RE: Circuit pressure

Are you certain all the air has been purged from the system?

Ted

RE: Circuit pressure

In SoFla, brown anole lizards will occasionally be found in a garden hose of ~15mm i.d.

Since there is a temperature difference around the loop, the location of a clog in the pipework might be found by a slow and careful temperature survey.  The other choice is pressure taps at the inlet and outlet of all components.

Speaking of which, I don't see an element that I can identify as a pressure gage or transducer.  Have you measured the actual pressure at any single point in the loop?  That might give you a clue about the actual operating point.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Circuit pressure

Have you check direction of rotation? - the pump might be installed corectly in terms of pipe work etc - check to be sure as it won't be the first time a pump has been run backwards.  

RE: Circuit pressure

Dear dianad Hello,
If you are confimed about the direction of rotation as "correct" (As this is most usually witnessed with wrong cable leads connection on three phase E/motor driven pumps)
Then try to check for physical obstruction alone on the Discharge/suction sides; may be through flush back and local draining if safe?

Best Regards
Qalander(Chem)

RE: Circuit pressure


Might want to look at the possibility that pump intake is being starved by inadequate available volume.
  

At 74th year working on IR-One PhD from UHK  - - -

RE: Circuit pressure

(OP)
Thank you all for the replies!

I'm more concerned about the air. Tha guy how made the installation used a filling pump witch has the possibility to remove the air durin the system filling. So, for this reason, he did not install an air purger at the top of the circuit. I wonder if some air could be formed during the time and this would be the problem....

I don't know where do i start to find the problem and oi don't know also what are the methods to look for them...

Thank you!

 

RE: Circuit pressure

Air could be a problem - seems that you need an air valve of some description at the high point, at least this eliminates one potential problem.  

RE: Circuit pressure

"Manometro" is Spanish for pressure gage, I think.  There's one on the pump outlet, and one on the downstream side of the...air exchanger?  Ought to be one on the pump suction, but hey.  Dianad, can you tell us what the readings from the various pressure gages is?

RE: Circuit pressure

"medidor de presión"  

"If stupidity got us into this mess, then why can't it get us out?" - Will Rogers (1879-1935) ***************
http://virtualpipeline.spaces.live.com/

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