How does a pump trade flow rate for head, i.e., pressure? 6

[Robert Clark]

A pump’s power is a product of its pressure rise times volume flow rate. Commonly, a pump is specified by giving the pressure rise, or head, it can provide and the flow rate, such as in gallons per minute(GPM).

But some pumps provide the user with a chart that shows how the pressure rise can be varied with a corresponding change in flow rate, inversely related.

This is what I need for my application. I need a higher head than what the specs say for the pump, allowing for the reduced flow rate. The specs don’t say whether or not these values can be varied. So is there some common method by which this is done for pumps with this capability?

I thought they just reduce the inlet size to change the flow rate, with an associated change in the size of the pressure rise. But then I thought this would just mean the pump would just suck harder on the water input source, making the flow rate stay the same.

So how do pumps with this variable capability do it, and can other pumps be adapted to also do it?

Robert Clark

 

[3DDave]

https://www.youtube.com/watch?v=aiE58Ri5axQ

I have no idea why there is a need for high pressure in the application that a drone is lifting the hose. Gravity works just fine to cause the water to fall. 3000 psi is, I think, nearly a mile of pressure head. That's a lot of hose, even considering flow losses.

Is it right to guess that this has nothing to do with drones or fire suppression and the example is chosen to hide the actual intended application but be close enough while still be misleading?

 

[1503-44]

The water jet is needed to look kool enough to be click bait for Shark Tank.
If it did a gravity dump, then everyone could see it takes 10 trips to put out a BBQ.

Do the spray paint thing.

 

[TugboatEng]

Those water jet packs are very low pressure, typically powered with an axial flow pump.

 

[Robert Clark]

3DDave, keep in mind the hose and therefore the distance from the water source to the location of the fire suppression, is VERY far away.

Now consider what kind of scenario where the only water source would be so far away, AND why the hose would have to be held so high aloft necessitating the very high head.

About the video you linked, yes. Instead of the hose being held aloft by drones, given sufficient pressure on the ground it could be held aloft by the force of the exiting water at the top.

Robert Clark

 

[1503-44]

Yes, hydrojet packs are low pressure, but have a high mass ejection rate, which causes the same reaction force as a low volume high pressure system.

 

[Robert Clark]

Better fitted with spray paint cans. I can't see it putting out enough volume to actually extinguish anything more than a fat Cuban cigar.

1503-44, those huge pumps I mentioned can put out 375 GPM. This compared to a common 2” fire hose which might put out 250 to 350 GPM:

#60 - Double Jacket Fire Hose Comparison: 2 inch Fire Hose vs. 1¾ inch vs. 1½ inch.
“2-inch double-jacket fire hose: large volumes, difficult handling
2-inch double-jacket fire hose weighs in at 40 pounds dry and flows up to 250 gallons per minute, making it 30 percent heavier (but 100 GPM faster) than the lightest hose. How does it handle? Paul Shapiro at Fire Rescue Magazine suggests that a single trained firefighter can handle a hose of this size—albeit with some effort:
[D]o we need to be standing up with a 250-gpm flow (or higher) handline taking a beating or is there an easier way? As a matter of fact there is an extremely easy way to move the water: Just sit on it! That’s right, one firefighter can in most cases handle flows up to 350 gpm on a 2" handline with no problem at all, sitting on the hose.”

https://www.qrfs.com/blog/60-double...rison-2-inch-fire-hose-vs-1¾-inch-vs-1½-inch/

The small pressure washer demos I was suggesting was only for proof-of-principle to show the VERY long distances are possible.

Robert Clark

 

[TugboatEng]

The purpose of water in fire suppression is cooling. Cooling requires mass. Quantity delivered is the most important metric when discussion water as a fire suppression agent.

 

[3DDave]

Keep in mind this started as a request to over-boost a consumer grade pressure washer. The goals keep moving.

Try filling out the following:

I need to deliver ___________ ________ (volume, units) per __________ _______ (time, units) of ___________(clean/dirty/contaminated/salt) water to an altitude of ________ ______ (distance, units) from a lateral distance of ________ ______ (distance, units) using an available power source of ________ ________ (power, units) in a way that uses a flexible temporarily installed hose.

 

[Robert Clark]

In addition to the application of fighting fires far away from any available water source, there is also this extremely important application:

https://www.worldvision.org/clean-water-news-stories/walk-water-6k

Robert Clark

 

[3DDave]

I'm out. There are already pumps designed for that purpose.
Is this a VPN account from Pakistan again? I hate those.

Interesting:

https://www.physicsforums.com/search/4522311/

And here is why this topic has dropped into here:

https://www.physicsforums.com/threads/minimize-supported-weight-of-a-water-pipe.1006338/page-2

 

[Artisi]

"I think you can see where I'm going with this." NO -- please fill us in .

I'm with 3DDave - a complete waste of time.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Robert Clark]

California firefighters ‘stretched to limit’ as devastating blazes become the norm.

https://apple.news/ARNc_w8E1QVu_TuCHsVxJhg

Robert Clark

 

[1503-44]

Drones need not apply.

https://m.youtube.com/watch?v=rkoQZvyc04I

Note no spray nozzles, hoses, gravity dump and VOLUME.

 

[LittleInch]

3Ddave - great spot.

Robert, if that is indeed your name, the issue is not finding a pump unit to do the duty, the issue is finding a drone big enough to lift up the hose and deal with all the forces involved when you flow liquid up a flexible tube.

To a certain extent, pressurising the hose will make it more rigid and help with reducing the end lift force, but if the pressure stopped then this would vanish and the drone land on someone.
fighting forest fires is not for something like this, but you could use them on fires in taller buildings to get water up and in a building, but that's what fire hoses do any way.

So I don't know where this post is going really.



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

 

[TugboatEng]

If these drones are intended to work on tall buildings, what tall building doesn't have a fixed firefighting system already installed?

 

[LittleInch]

Those many without sprinkler systems.

Once it catches fire you might not be able to get to floors on fire.

But that's what fire hoses do anyway.

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

 

[Robert Clark]

That video is of airplane water or fire retardant drops which are only minimally slows the spread of the large forest fires.

 

[Rputvin]

Jumping in a little late -

So the main question is to move water some "very far" distance, with a hose, and a drone, pumped at "very high" pressure, with "very little" flowrate?

You realize every increase in distance will make the hose need to be stronger (heavier), as with every incremental increase in pressure will require the hose to be stronger (heavier), and the stress of high pressure in a larger hose vs. a 1/4" pressure washer line will need more strength (heavier).

So you're stringing a heavy, high pressure line potentially "very far" (miles?) across what kind of land, or homes, or whatever, with a drone.

And, since you're trying to use the force of the water flow to reduce drone load, you're proposing to have this ON THE ENTIRE FLIGHT? So you've got a few thousand feet of reeled up high pressure 1.5" hose that also need to be accounted for in terms of practical application of this idea.

Does the FAA know you're planning on flying a drone large enough to carry several hundred pounds (which is definitely within their scope of oversight and regulation), with a hose a few miles long, into a heavy air traffic and dangerous location? I think they'll want to know sooner rather than later, and their response will have a large impact on the viability of this endeavor.

You're commended for trying to make something that will help people and make the firefighting job around rural forest fires easier, but I think this needs some serious reality check before you keep trying to plow forward.

 

[Rputvin]

Oh, and I would consult with firefighting services experienced in forest fires to determine what actual flowrate you need to target, which would actually define one of the major missing parameters you keep ignoring.

Once you have a flowrate - define your max distance. This will determine the hose size and required pressure to overcome friction loss and deliver the needed pressure at the nozzle to spray the water. From there a hose can be sourced, and its real values for weight can be used in your drone load calculations instead of just looking at other examples and trying to copy their work as much as possible. The internal volume of that real hose can also then be calculated to determine an actual system weight the drone would need to support.

And yes, it needs to support the ENTIRE WEIGHT, not a reduced weight from partial use of flow/pressure to reduce drone load - you cannot count on the pump functioning, and building failure into your design is very much necessary. (edit; which brings up a point regarding what happens if the drone fails, or the hose gets snagged on something and brings the drone down or detaches the hose. How many roads will you be blocking, how many power lines will have hose draped over them, how many homes will you damage in this event?)

Once flow and pressure are established a pump can be sourced.

After all of those puzzle pieces are in place you MIGHT actually get some help from forums full of people trying to help you. You're not making it easy.

 

[Artisi]

Rputvin, don't stress about it, it's all airy fairy nonsense anyway, it will never fly (excuse the pun)

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)