(Somewhat unexpected) Pressure Rise 2

[zaphod1]

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,

 

[quark]

Thanks 25362,

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.

 

[katmar]

25362, in order for the pressure drop between the filter and the lower header to be greater than the pressure drop between the filter and the upper header either the flow to the lower header must be higher, or the piping to the lower header must have greater resistance.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[25362]

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.

 

[zaphod1]

Is it possible that the pipe coming from the pump is not full? The pump curve shows 288 GPM @45ft-hd. I have a pressure drop across the filter of around 2.7 psi, which is what the filter manufacturer says is the appropriate head loss at that gpm. The pipe from the pump is a 6' vertical rise before it turns into the filter. The assembly is very much like the drawing in danw2's reply. The reason I ask is because I have been trying to use a ultrasonic flow transmitter to measure flow on this riser, and while the valves are 100% open I have 0 signal strength. Only after I throttle the valves upstream from the nozzle assemblies can I achieve a useable signal. Just thought I would add more confusion to my already confusing questions.

Thanks,

 

[25362]

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://www.omega.com/prodinfo/ultrasonicflowmeters.html

 

[rconner]

Based only on the approximate profile appearance of what is drawn, is it possible the pressure at the lower elevation gauge during flow is simply reduced by loss of head through the apparently multiple nozzles (orifices) to atmosphere that appear in front of the gauge (some unlike the other gauges)?
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?)

 

[zaphod1]

I have calculated the velocity of the water (at 288 gpm) to be around 13.07 fps and the pipe i.d. is 3". The density of water is ~62 lbs/cu.ft with a viscosity of 0.470cp at 140 degrees F. I come up with a Reynolds number of 646,000. Can someone double-check me? If this is the case, isn't this a guarantee of turbulent flow?
Thanks,