flow rate vs pressure vs velocity

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sooooooo, i helped build a piece of equipment that im not happy with.the goal is to blast crap out of 1/4" screen, as the pieces to be cleaned very slowly conveyor through what is basically a scaled down car wash. build headers with spray nozzles, supply nozzles with pressure to obtain crap-blasting velocity, water is to be recycled.pump supplier wants to know suction head pressure, which aint much, so they supply a relatively small pump.. . . .that wont cavitate. guaranteed and waranteed.i dont have velocity needed to blast crap, so, i have taken matters into my own hands. which means i have confused myself. residual pressure in the header, with all nozzles spraying, is a measly 20 psi. but maybe 20 psi is good? maybe the orifice size of the nozzles would restrict flow enough that 40 psi would achieve nothing more than atomization, without a respectable increase in velocity? maybe the flow rate of the pump would do better with larger orifices, and thereby increasing velocity?or maybe we need a different pump, but with the lack of suctiion head, would grenade n a few years? but considering the man-hours required to re-wash, maybe its cheaper to replace the pump every few years?2 pumps in-line?currently using centrifigal, but maybe this example is best suited to positive displacement? i feel bad that i sold this piece of equipment to family, and though it works better than the antique they had, i feel this new one should be aw-inspiringly awesome at blasting crap. but im just a fabricator, not an engineer. i relied on the office to take care of the math, and they failed.im imagining a line that separates pressure= velocity vrs flow-rate= velocity, and both hate but require restriction to increase velocity, until restriction reduces velocity.do i need a new pump or new nozzles, and how do you knowbosses stuff:trailblazer 325maxstar 200my stuff:sa 200fronius transpocket 180100 amp Lincoln w/f97 f350 DITKevin
Reply:Do you have information on pump?With a pump curve you could determine ideal operating point.Or by knowing impeller diameter and rpm,max pressure couldbe calculated.(approximately)20 psi sounds low. Maybe too much nozzle for pump?Have you tried removing nozzles and plugging holes tosee if pressure increases?If pump isn't cavitating,we can probably rule out a suction side/supply problem.Can't help you with nozzle/velocity calculations.Miller a/c-d/c Thunderbolt XLMillermatic 180 Purox O/ASmith Littletorch O/AHobart Champion Elite
Reply:

Originally Posted by 92dlxman

sooooooo, i helped build a piece of equipment that im not happy with.the goal is to blast crap out of 1/4" screen, as the pieces to be cleaned very slowly conveyor through what is basically a scaled down car wash. build headers with spray nozzles, supply nozzles with pressure to obtain crap-blasting velocity, water is to be recycled.pump supplier wants to know suction head pressure, which aint much, so they supply a relatively small pump.. . . .that wont cavitate. guaranteed and waranteed.i dont have velocity needed to blast crap, so, i have taken matters into my own hands. which means i have confused myself. residual pressure in the header, with all nozzles spraying, is a measly 20 psi. but maybe 20 psi is good? maybe the orifice size of the nozzles would restrict flow enough that 40 psi would achieve nothing more than atomization, without a respectable increase in velocity? maybe the flow rate of the pump would do better with larger orifices, and thereby increasing velocity?or maybe we need a different pump, but with the lack of suctiion head, would grenade n a few years? but considering the man-hours required to re-wash, maybe its cheaper to replace the pump every few years?2 pumps in-line?currently using centrifigal, but maybe this example is best suited to positive displacement? i feel bad that i sold this piece of equipment to family, and though it works better than the antique they had, i feel this new one should be aw-inspiringly awesome at blasting crap. but im just a fabricator, not an engineer. i relied on the office to take care of the math, and they failed.im imagining a line that separates pressure= velocity vrs flow-rate= velocity, and both hate but require restriction to increase velocity, until restriction reduces velocity.do i need a new pump or new nozzles, and how do you know
Reply:thanks guys, i did get the graph for this specific pump, and am in the process of trying to figure it out.its not so much out of dire need but more for fun that i figure this out.if i ever do, ill post up, but i think from your guys' posts, i have established my goal.find highest efficiency on curve for pump, and then size nozzles to achieve highest velocity before pump efficiency (flow-rate) is diminished to the point of not providing flow enough to MAINTAIN acceptable velocity. which i think would relate to droplet size.i am thinking of the fogging systems i have helped with. residual header pressure is a WHOPPING 1000 psi, but the orifice restricts flow so much that what comes out the nozzes comes out like, well, a fog i guess.bosses stuff:trailblazer 325maxstar 200my stuff:sa 200fronius transpocket 180100 amp Lincoln w/f97 f350 DITKevin
Reply:Most mfg'rs of the nozzles have charts that show flow rate(GPM or LPM) at different pressures which combined with the number of nozzles will help determine pump volume at the desired pressure.                                        MikeOl' Stonebreaker  "Experience is the name everyone gives to their mistakes"Hobart G-213 portableMiller 175 migMiller thunderbolt ac/dc stick Victor O/A setupMakita chop saw
Reply:@ 92dlxman - do not completely understand your requirements and/or your exact application. Anyways, run this nozzle selector iSpray tool from Spray Systems Co (Wheaton, IL). If you want to further explore Bernoulli and Continuity in action, check out their flow rate calculator from the SprayWare tools.Understanding the basics of flow/pressure by studying the pumps curves, as you did, is the right call. Straightforward. You should be in the 1-2ksi range, as a guesstimate, for your application.As an aside, modern CNC cutting tables are running direct drives and hydraulic intensifiers to achieve a 60-90ksi pressurized water/garnet jet. However, 'power at the nozzle' is more relevant than total pressure.Last edited by ManoKai; 01-31-2017 at 03:19 AM."Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:20 psi sounds stupid low.  That's barely even "rinse" territory.  Residential water is in the 50 psi ballpark.  You weren't specific in what you are washing, but maybe you need nozzles on both sides of the screen.  Stuff like grass will survive a couple thousand psi from one direction when tangled in a screen.My name's not Jim....
Reply:One thing that is missing from your thought is time.The Grand Canyon was carved out with very little pressure and velocity(relatively speaking) but a whole lot of time.
Reply:

Originally Posted by 92dlxman

sooooooo, i helped build a piece of equipment that im not happy with.the goal is to blast crap out of 1/4" screen, as the pieces to be cleaned very slowly conveyor through what is basically a scaled down car wash. build headers with spray nozzles, supply nozzles with pressure to obtain crap-blasting velocity, water is to be recycled.pump supplier wants to know suction head pressure, which aint much, so they supply a relatively small pump.. . . .that wont cavitate. guaranteed and waranteed.i dont have velocity needed to blast crap, so, i have taken matters into my own hands. which means i have confused myself. residual pressure in the header, with all nozzles spraying, is a measly 20 psi. but maybe 20 psi is good? maybe the orifice size of the nozzles would restrict flow enough that 40 psi would achieve nothing more than atomization, without a respectable increase in velocity? maybe the flow rate of the pump would do better with larger orifices, and thereby increasing velocity?or maybe we need a different pump, but with the lack of suctiion head, would grenade n a few years? but considering the man-hours required to re-wash, maybe its cheaper to replace the pump every few years?2 pumps in-line?currently using centrifigal, but maybe this example is best suited to positive displacement? i feel bad that i sold this piece of equipment to family, and though it works better than the antique they had, i feel this new one should be aw-inspiringly awesome at blasting crap. but im just a fabricator, not an engineer. i relied on the office to take care of the math, and they failed.im imagining a line that separates pressure= velocity vrs flow-rate= velocity, and both hate but require restriction to increase velocity, until restriction reduces velocity.do i need a new pump or new nozzles, and how do you know
Reply:An industrial triplex pump costs between 600 and 2,000 bux, so maybe, as William mentioned, adding an air compressor, which cost less would be the way to go. You won't need as much water if you run with 80psi of air to your header supplied with just tap water or a gravity drain water tank. Just a thought...