(Somewhat unexpected) Pressure Rise
(Somewhat unexpected) Pressure Rise
(OP)
I have a parts washer system that uses a vertical centrifugal pump to deliver a heated, 97% water solution up to the top of the washer through a 3” pipe, then distributes (branches) into two 3” pipes. One of these pipe branches delivers water to 21 nozzles, with an equivalent orifice size of 0.203” each, that spray down on to parts passing under the nozzles. The other pipe delivers a similar system that sprays the water on the under side of the part. The pump pressure on the down-stream side of a filter is around 12psi. On the branch that feeds the nozzles spraying downwards the pressure is consistently around 0.25 to 0.5 psi higher. Coming from the pump the water raises around 5 feet, then after passing through a horizontal filter, the pipe drops approximately 18” then branches and drops a further 18” to the downward nozzles and approximately 36” to the upward spraying nozzles. The upward facing nozzles are typically around 10 psi. What could cause a pressure rise, other than gravity, in the branch that feeds the downward facing nozzles?
Thanks,
Thanks,





RE: (Somewhat unexpected) Pressure Rise
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: (Somewhat unexpected) Pressure Rise
I have installed 0.25% FS accuracy (30 psi span) transmitters, I also see this effect on the less accurate dial-type gauges that are installed at these locations.
Thanks,
RE: (Somewhat unexpected) Pressure Rise
The inaccuracy of the transmitters is only 0.075psi. Mechanical gauge accuracy depends on model and can be as bad as 3% (0.9 psi on a 30 psi gauge)
It appears that your 12 psi measurement is at the highest elevation point.
The 12 psig is downstream of the filter. The filter location must be at the top point of elevation since "coming from the pump the water raises around 5 feet, then after passing through a horizontal filter". Everything else drops from that point.
The downward spray nozzles are 36" below (18" drop + further 18" drop) that top elevation measurement point.
The upward spray nozzles are 18" below the downward nozzles.
Gravity adds a psi for every 27.7" of elevation, and you have a 36" elevation drop to the downward spray nozzles. So an increased pressure makes sense.
But the upward spray nozzles are 18" lower in elevation than the downward nozzles, yet are 2psi lower than supply.
I'm still scratching my head. Have I missed something in the sketch?
Dan
RE: (Somewhat unexpected) Pressure Rise
Flow distribution in dividing (as well as in combining) branched manifolds may be nonuniform, affecting static pressure measurements due to the different impedance characteristics of each branch.
RE: (Somewhat unexpected) Pressure Rise
RE: (Somewhat unexpected) Pressure Rise
The pressures read at the two spray headers are lower than they would be if static head was the only consideration. Obviously there are friction losses after the first pressure point, and these losses explain why the header pressures are lower. Without knowing in detail the pipe lengths and numbers and types of fittings it is impossible to comment on whether the losses observed are in line with expectations.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: (Somewhat unexpected) Pressure Rise
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RE: (Somewhat unexpected) Pressure Rise
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RE: (Somewhat unexpected) Pressure Rise
Thanks
RE: (Somewhat unexpected) Pressure Rise
The upper PI and PT are in 2" line prior to any spray nozzles, and the lower PI and PT are in 3" line prior to any spray nozzles.
Good luck,
Latexman
RE: (Somewhat unexpected) Pressure Rise
2" valve 2-1/2" valve
2" pipe 3" pipe
3x2 reducer 3x2-1/2 reducer,
and we're looking for 2 psi? Its in there somewhere.
Adios muchachitos.
Going the Big Inch!![[worm] worm](https://www.tipmaster.com/images/worm.gif)
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RE: (Somewhat unexpected) Pressure Rise
Thanks,
RE: (Somewhat unexpected) Pressure Rise
This may not be exactly what you have, but it's probably in the right order of magnitude.
Good luck,
Latexman
RE: (Somewhat unexpected) Pressure Rise
The gauge after the filter reads 12 psi, and if the 36" drop down to the downward spraying header added its full static head the gauge on this header should read 12+1.3 = 13.3 psi. However, it actually reads between 12+0.25 and 12+0.5 psi. Call this pressure 12.3 psi. We expect 13.3, but actually get 12.3, so we have losses of 1 psi.
If I calculate the flowrate through a 3x2 reducer and a 2" globe valve to give a 1 psi pressure drop I get about 45 gpm. If the valve is a ball valve rather than a globe the flowrate would have to be 170 gpm to give 1 psi loss. Both of these estimates are way lower than Latexman's 400 gpm, but I suspect that Bete's definition of "free passage" is the largest particle size that can pass through, rather than the orifice size. You would never get 21 gpm through a 0.2" orifice at 10 psi.
Unless we know exactly what the length of 3" and 2" pipe is, the number and size of all the fittings and the type of valve we cannot give a definitive answer. But we can say that the answer looks to be in the realms of the possible.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: (Somewhat unexpected) Pressure Rise
Best Regards,
RE: (Somewhat unexpected) Pressure Rise
Good luck,
Latexman
RE: (Somewhat unexpected) Pressure Rise
The pressure gauge after the filter should indicate the resistance offered to the flow by the pipe section after the gauge. If the elevation is supplementing the the pump pressure, that should replicate in the gauge reading after filter, unless there is siphoning effect. Otherwise, I am not getting any reason for the filter gauge reading to be lower than that of header gauge.
May be I am wrong.
RE: (Somewhat unexpected) Pressure Rise
Indeed the pressure readings on the branches are supposed to show the friction drops through their downstream spray nozzles.
Since the lower upward-spraying header shows 10 psig while the upper downward-spraying header shows 12.25-12.5 psig, assuming type, degree of cleanliness, and number of nozzles, are equal, it could mean that the flow on the upper branch is greater. Which would confirm the original assumption of flow uneven distribution.
RE: (Somewhat unexpected) Pressure Rise
Quark, on gas-free liquid flows, beside the downstream friction resistance effects, the gage reading after the filter could be greater or lower than those of the downstream gages depending on whether the flows are upward or downward (due to gravity), and the pipe diameters don't change velocity heads into pressure heads. I think we talked about this in past threads.
RE: (Somewhat unexpected) Pressure Rise
Sometimes I become too stupid, may be due to graying hair or becoming too busy with nontechnical work. I just came to correct my post and fortunately saw your comment.
RE: (Somewhat unexpected) Pressure Rise
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: (Somewhat unexpected) Pressure Rise
Katmar, I agree. I'll go for your second option, which could be justified by an increased pipe length and more fittings between PI 103 and PI 105.
Besides, we still don't know whether any dirt -and for that matter what kind and size of dirt- may be present in the system downstream the filter, and in what branch (and fittings) would it tend to collect. The fact that a filter has been installed to protect the nozzles hints to the possible fouling of the system.
RE: (Somewhat unexpected) Pressure Rise
Thanks,
RE: (Somewhat unexpected) Pressure Rise
Ultrasonic flowmeters have their own idiosyncrasies, some need particles or bubbles in the stream, others need turbulent eddies.
They sometimes suffer because the signal gets carried away beyond the receiving sensor; although they are pointed against the direction of flow, they are affected by installation air gaps, the piping material of construction, etc. For details, see, for example,
http:
RE: (Somewhat unexpected) Pressure Rise
With regard to the originalquestion-- also particularly/perhaps if the operation of this system is some intermittent, is it possible say that air is in the system, say by water draining out the nozzles as the systemis shut-down for any reason (and be replaced by some entering, ambient temperature air?) You of course mentioned that the water pumped into the piping to do the washing is "heated" -- if there is cool air at times in the system, is it possible that heating this air without rapid relief of pressure by the orifices might result in some increase in pressure per "Charles Law" (of course at least until the systemreaches equilibrium or the air is scavenged from the system?)
RE: (Somewhat unexpected) Pressure Rise
Thanks,