Circuit pressure

[dianad]

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!!

 

[MikeHalloran]

Where is the vent to atmosphere?



Mike Halloran
Pembroke Pines, FL, USA

 

[BigInch]

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)
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[dianad]

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!

 

[BigInch]

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)
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[dianad]

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

 

[BigInch]

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)
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[hydtools]

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

 

[BigInch]

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)
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[quark]

I saw a dead rat but never an armadillo.

 

[BigInch]

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)
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[Artisi]

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.

 

[BigInch]

#1 on my list above.

"Make everything as simple as possible, but not simpler." - Albert Einstein (1879-1955)
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[dianad]

I everyone.

It can not be rats or gloves, etc, because is a 15mm pipe.
The pump is installed correctly. I've attached a scheme.

I'm quite lost. The 1st think that i thought is to change the pump, but i'm affraid that may not be this the reason.

 

[hydtools]

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

Ted

 

[MikeHalloran]

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

 

[Artisi]

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.

 

[786392]

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)

 

[Apakrat]

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 - - -

 

[dianad]

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!