indirectly electrical

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iceworm

iceworm

Curmudgeon still using printed IEEE Color Books
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Charlie's idea of a broken pipe is a good place to start.

ptonsparky said:
Next week they have some down time for checks.
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Interesting. From what you are telling us, the system is not working now. I would have suspected they have downtime on this system right now.

ptonsparky said:
Pressure gauge at outlet of booster pump reads zero on a 0-60 lb gauge with water on, no pump.
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First: Has this system ever worked before? Or never worked since startup?

Second: Is the booster pump a positive displacement or a centrifigul?

Thirde: When you say, "water on", does that mean the valve at the booster pump suction is OPEN?

Assuming: valve open, centrifigul pump, no flow at nozzles:
The pressure at the pump discharge should be the same as the pressure at the 2"CU feed. No flow = no pressure drop. If this is the case, the valve is not opening, or is plugged.

If the booster is a PD, then interpretation of the symptoms is different

charlie b said:
Something is not adding up here.
Click to expand...

Hummmm - ya' think

ice
 
ptonsparky

ptonsparky

Tom
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EC - retired
No boken pipe, we would notice.
System is fed from a submersible we but a vfd on a year or so ago. No transducer. It hits 30 hz at start, runs there for a minute or so then is allowed to slowly ramp to 60hz where it stays until demand drops & press sw opens. The way they wanted it. Don't remember the hp but it feeds the building via a 3 1/2" OD pvc. 70' give or take. After the pressure tanks a manifold reduces our pipe to 2" copper. Maybe 50'. 4 90s that we know & doubt more.

I have not seen it operate but have been told it did before the vfd.
Water does flow thru the nozzles with the pump off and valve on, pressure does not raise enough for guage to noticable change. 64 nozzles rated @ 1/2 gpm, 40 psi thus the need for 32 gpm ( now don't remember if it was 68 and 34). Did not look to see if all were spraying.

Centrifugal pump.

They would like more pressure but this will not keep them from shipping taters. I do not know what the working pressure of the diaphram type valve is nor its gpm. We can work on it & other projects usually after 2:30.

There is more to making tater chips than slicing & frying. One of the reasons I like what I do, plugging & switching all day would kill me.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
charlie b said:
I got it from my local friendly plumbing engineer, who got it from one of those "sliding wheel design tool thingies" (we have similar sliding tool thingies for motor design and other electrical stuff). Does your source have a table for copper pipe, similar to the schedule 40 steel pipe?
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No. It does not.

However, in this reference?The Copper Tube Handbook?on page 30 is a table which lists 2" Type K, L, and M pressure drops at 0.012, 0.011, and 0.010 psi per linear foot respectively for 35GPM flow rate... not much difference between copper and steel.

On page 32 of the same reference, is a table titled "Pressure Loss in Fittings and Valves Expressed as Equivalent Length of Tube, feet". With these figures, you just add the amount given for the type of fitting or valve, each, to the length of the run to get an equivalent overall pressure drop. pressure drop, or gain, result from elevation changes also need to be figured in to the overall pressure drop.
 
iceworm

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
ptonsparky said:
No boken pipe, we would notice.

After the pressure tanks a manifold reduces our pipe to 2" copper. Maybe 50'. 4 90s that we know & doubt more.

I have not seen it operate but have been told it did before the vfd.

Water does flow thru the nozzles with the pump off and valve on, pressure does not raise enough for guage to noticable change.

Centrifugal pump.

I do not know what the working pressure of the diaphram type valve is nor its gpm.

plugging & switching all day would kill me.
Click to expand...

Hummm ..... So here is what we think we know:

it has worked before, so something changed (or broke).

You have checked the pressure at the Pressure Tanks and it is 85 psi?

50' and 4 - 90s, 2" CU isn't much for the 34gpm. That should be okay.

Other than the 2" valve at the booster pump suction - no other valves that could be accidently left pinched down?

The pressure gage you are reading is on the booster pump suction.

I'm glad you knew how to spell "centrifugal"
------------------

So, my guesses would be right along with your first thoughts: You are looking for a restriction causing a large pressure drop between the pressure tanks and the booster pump suction.

As you said, the valve is suspect - not opening completely or plugged with debris.

Or possibly the booster pump suction is plugged with debris.

As long as the pressure rank is at 85psi, I would not suspect the VFd or well pump.

ice
 
H

hardworkingstiff

Senior Member
Location
Wilmington, NC
I'm a little slow, so be patient.

I'm of the understanding you have a submersible pump with a VFD controller pumping water to a "booster" centrifugal pump that feeds the nozzles.

You see no noticeable increase in pressure/flow when the booster pump comes on.

I wonder (just a shot in the dark), since it allegedly worked before the VFD controller was installed, maybe the VFD controller is the culprit?

The reason I think this way is my understanding of how the VFD controllers for the submersible pumps in the gas/diesel tanks work at gas stations. The controller will vary the pump speed based on the work the controller sees the pump doing. The more work it sees the pump doing, the more it speeds it up. So, what happens when you kick on the booster pump? The booster pump pulls a suction on the discharge side of the submersible pump. This in essence would look to the VFD controller as if the submersible did not have much of a demand on it so the controller would slow the submersible down and thereby counter any increase in flow the booster pump was producing?

If this sounds ignorant, sorry. I don't really have any experience with VFD controllers except at gas stations.

Edit: You really need those pressure gauges on each side of the booster pump.
 
charlie b

charlie b

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Location
Lockport, IL
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Retired Electrical Engineer
I think we will all agree that when something no longer works (i.e., something that did work in the past), a good troubleshooting technique is to look into whatever changes were made most recently. In this case, I will agree with those who would focus attention on this:
ptonsparky said:
They want to use a pressure switch on the input of this pump to turn it on. We have that done.
Click to expand...
It could be the valve's control signal, or perhaps it is set up to sense pressure on the wrong side of the valve. But my money is on a mechanical failure within the valve itself.
 
H

hardworkingstiff

Senior Member
Location
Wilmington, NC
After rereading this thread I see my posts (other than the pressure gauges being required to properly troubleshoot) are just plain.................. dumb.

Like Charlie, when was the last time this worked properly and what was done (if anything) between then and now?
 
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