Pump to generate vertical stream of water from nozzle.

[jcoeng]

Hello, I need to build a pump/pipe system to generate a 6m high stream of 50C water from a 6.4mm nozzle. Hoping to use one of the gas powered pumps from Harbor Freight but want to make sure it can do the job before purchasing.

I've been working through basic bernoulli calcs but I'm definitely missing something and really need some help.

The specs on the pump I'm looking at are given as 35gpm, 1in outlet, 65ft Maximum Head Lift and 19ft Intake Head lift.

The current idea is to connect a garden hose to the pump and then do the final nozzle reduction at the end of the hose. I understand there are a lot of losses in the system but I'm not looking to hit an exact number, just see if the pump will work and likely if I can't reduce throttle/output I'll bleed off some of the output. Can anyone walk me through the process to verify the pump performance in terms of the desired output?

Thanks for your time.

 

[LittleInch]

Forget Bernoulli, useless at real life calcualtions.

If you're trying to create a fountain for some reason ( in other words zero velocity at 6m from your nozzle), I reckon your 6.4mm ( aka 1/4") nozzle needs a velocity of about 12 m/sec allowing a bit of aerodynamic losses. That equates to about 6 US GPM, so your pump look Way too big.

How much pressure?

You need to work out the losses, but there will be a fair bit across a small nozzle.

The 19ft I assume is lift height to pump out something - you don't need this.

Just find the differential head and add the inlet head.

Only when you know all the inputs can you determine if your pump is man enough or not.

What is this thing? a 6.4mm jet is going to be quite hard to keep as single column of water and not spread out over 6m.
I'm sure you can just go and buy a fountain that gives you a jet 6m high???



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LittleInch]

https://www.water-garden.co.uk/prod/grand-high-jet-fountain-nozzle-for-pro-jet-floating-fountains

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

Based on this chart, you would need a 10 mm nozzle to obtain a height of 6 meters:

Smooth Bore Fountain Nozzle

The pump head required is 9 meters (29.5 ft.) with a flow of 57.1 l/min (15 gal/min.). To that head, I would add 10 feet for miscellaneous pipe losses.

Your pump is too large and your hose is too small. Size the pump based on the fountain nozzle performance specifications. Use at least a 1-Inch diameter pipe, which will probably be adequate unless the pipe run is very long.

 

[jcoeng]

Thanks for all the replies! I purchased the pump and tested. It far exceeds the required minimums for the spec.

The spec doesn't call for a continuous aligned flow column of water, only a jet of water exiting a 6.4mm nozzle achieving a height of 6m. To me that says it can be spread out as long as water reaches that height. For my test I'll be shooting higher to ensure I exceed the minimums on the spec.

The test is for DO-160 environmental testing for "continuous stream waterproofness test". I'm testing a device that will be mounted on the outside of an aircraft where it will be subject to deicing and pressure washing. Tests will be performed at my home, so no long pipe runs and no real pre-configured equipment available since its a unique application. Therefore trying to use OTS components. short 6' 5/8" hoses, one for inlet and one for output, both necked down from the 1" size. Found the perfect size garden hose nozzle at the local hardware store. The part that sucks is running the test with a gas powered pump, its loud and can't ship the setup easily. Ideally I'd be able to re-create the setup using a variable flow electric pump but haven't done enough digging into this option, I needed to have it build over the weekend and get back into testing.

For the actual test I'm filling up a 45gal reservoir (technical name for a big trash can from home depot) and pumping form that. Each orientation tested needs to be subject to the stream for 5min. In that 5min I'm draining the entire reservoir and have to keep the hose cranked open to achieve a slight negative from the start point.

As for requirements calcs. When working backwards I too got approx 36ft/s at the nozzle and a required Q of approx 6gpm. However when working form the pump specs to see what was possible is where I couldn't make it work with reasonable numbers, calculating a V(i) of 225ft/s using Q=vA and H of 789ft using projectile motion calcs h = v^2/2g. It took me a min but I did notice that when I fired up the pump and achieved max throttle/Q, I was not shooting 789ft in the air. The actual height was closer to the rounding error than the calculated height. Where do these equations break down. Pressure losses where Q1 =/= Q2 ?

I've got a working setup but still curious on how to perform the calcs to be reasonably close to the real world results.

 

[bimr]

Hoses have very poor hydraulic properties and therefor will have high pressure loss with lower flow than the equivalent pipe size. The diameter of the hose that you are using is too small for the flow and will limit the maximum height that the stream is capable of achieving.

You will never get a velocity of 225 ft/sec out of the nozzle as the pressure drop across the nozzle will be too high and the flow will be restricted.

 

[LittleInch]

jcoeng,

You are confusing what the pump can do and what it is actually doing.

I'm going to take a guess here, but I suspect your pump is a centrifugal pump of some sort. The characteristics of that pump are that it creates in essence a constant pressure give or take 10%. The amount of FLOW that you get is limited by the frictional losses of the system downstream of the pump, i.e. your hoses and the nozzle.
Even if this is some sort of Positive displacement pump, the pressure will be limited by a pressure relief valve in the pump system which will also limit the pressure available and the flow out, most of which is then simply going back to the inlet.

The nozzle will increase flow and velocity as you increase pressure, but the impact of more pressure reduces as the flow increases due to the v[sup]2[/sup] friction effect. Also your 6.4mm nozzle is acting like an orifice and at a certain pressure drop this hits critical flow, whereby you can't get any more flow through the orifice regardless of upstream pressure.

From your data you are actually pumping at approx. 9 GPM ( 45gal tank / 5 mins to empty it)

Thus your velocity through your nozzle is not 225ft/sec , but more like 50 ft/sec.

BTW what do you mean by "have to keep the hose cranked open to achieve a slight negative from the start point." Slight negative of what, where?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

Regarding aviation, there have been several incidents where pressure washing the aircraft pitot-static system caused the crash of the aircraft.

https://www.aopa.org/training-and-s.../hosed-did-sloppy-wash-job-cause-cirrus-crash

https://www.airspacemag.com/videos/category/new-label/why-inoperative-plane-sensors-can-leave-pilo/

One would think that a system designed for aviation usage would require more rigorous design and testing.

 

[jcoeng]

@LittleInch

Thanks for the reply with more detail. I don't have much experience with pumps as you can probably tell but this still felt like one of those conditions where real life =/= textbook ideal conditions for things to work nicely. Again probably just my understanding causing that feeling more than the conditions.

Agreed on your numbers. Will also add an inline pressure gauge before the nozzle to see where the pressure is at per stream distance.

The comment" have to keep the hose cranked open to achieve a slight negative from the start point" refers to having to keep the house supply water hose turned on filling the reservoir while pumping from it and at the end I still have less water in the reservoir ("negative") than when I started.

@bimr

I can't speak to the tests required for that equipment but I do know that even bugs/spiders crawling into pitot tubes or bugs hitting and clogging on takeoff have also caused crashes. The pitot tubes have caps that you are supposed to keep installed when in storage/pressure washing etc to help mitigate those risks but still seems odd that the people washing the aircraft and the pilots wouldn't be more aware of that condition.

Our system is not flight critical, meaning our device could fall off and the plane would still fly. It's actually part of our requirements to analyze what would happen if it fell off, got struck by lightning, etc. but again can't speak to what the required tests are for other devices/equipment on an aircraft and how adequate they are, but I will say that the FAA has done an incredible job setting specs for this stuff. The system is actually really interesting as many aircraft products are self certified. Meaning the FAA does not certify the product but certifies that you as the manufacturer have followed all of the specs. Those specs focus on ensuring the manufacturer has process in place and follows them to achieve air worthiness.

 

[77JQX]

jcoeng - in the cals that results in 225 fps velocities, the kinetic energy of the exit stream was likely neglected. It's a common mistake, because kinetic energy is usually negligible in hydraulic applications. Once kinetic energy is accounted for there should be better match between calcs and real world.

 

[cvg]

calculating a V(i) of 225ft/s using Q=vA and H of 789ft

[ul]
[li]the first mistake was the assumption of flow rate - pumps operate on a curve and 35 gpm and maximum of 65 feet of head are two points on that curve. correct flow rate is obtained through iteration.[/li]
[li]that bad estimate of flow rate led to a gross over-estimate of the velocity[/li]
[li]resulting in a completely impossible estimate of head[/li]
[/ul]