Plumbing question

[Myka]

Originally Posted by Reefer Rob

I think you're getting confused. Decreasing the pipe diameter will increase back pressure at the pump, but I don't think you can use it to increase PSI at the outlet that way. Think of the applications for that kind of technology Perhaps you're thinking of velocity? I'm not sure what that has to do with head pressure though, which is influenced by gravity, not a pump.

Maybe I'm not being clear about what I mean, or maybe you're wrong.

We use say 1200 psi to go through a 5/8" hose then through a 1/8" fitting on the end (we use this on Hydro-Vac trucks to cut the ground), and voila! It will cut your toes off. If we use 1200 psi pumped through a 3" hose (which you would never be able to hang onto, and you'd need a muuuuuuuch bigger pump to get 1200 psi out the end of a 3" hose), and you wouldn't hurt your toes with it.

So...slap your fancy words (pressure, head pressure, velocity, psi, flow, whateeeever) on that equation, and tell me what the heck you mean that I am wrong.

[golf nut]

Originally Posted by Myka

Maybe I'm not being clear about what I mean, or maybe you're wrong.

We use say 1200 psi to go through a 5/8" hose then through a 1/8" fitting on the end (we use this on Hydro-Vac trucks to cut the ground), and voila! It will cut your toes off. If we use 1200 psi pumped through a 3" hose (which you would never be able to hang onto, and you'd need a muuuuuuuch bigger pump to get 1200 psi out the end of a 3" hose), and you wouldn't hurt your toes with it.

So...slap your fancy words (pressure, head pressure, velocity, psi, flow, whateeeever) on that equation, and tell me what the heck you mean that I am wrong.

I think the pump comes into play here, I agree with what you can do to cut my toes off (God forbid) but you are using a positive displacement pump that doesn't know the meaning of the word backpressure, a typical aquarium pump doesn't come close to 3 psi and simply doesn't do what a hydraulic pump is capable of, in effect you are both right.

[sphelps]

Originally Posted by Myka

Maybe I'm not being clear about what I mean, or maybe you're wrong.

We use say 1200 psi to go through a 5/8" hose then through a 1/8" fitting on the end (we use this on Hydro-Vac trucks to cut the ground), and voila! It will cut your toes off. If we use 1200 psi pumped through a 3" hose (which you would never be able to hang onto, and you'd need a muuuuuuuch bigger pump to get 1200 psi out the end of a 3" hose), and you wouldn't hurt your toes with it.

So...slap your fancy words (pressure, head pressure, velocity, psi, flow, whateeeever) on that equation, and tell me what the heck you mean that I am wrong.

Adding a nozzle will increase dynamic pressure within the nozzle and increase the head pressure on the pump, but this will result in less flow on a centrifugal pump. In addition as stated positive displacement pumps are not effected by head pressure, they pump the same amount of fluid no matter what. Of course they do have a maximum operating pressure before something blows up which is why such pumps will have a release valve for safety.

You can't relate such systems to aquariums, we use centrifugal style pumps where head pressure is relevant, I'm actually pretty confused on what you argument is at this point

[Myka]

Originally Posted by sphelps

I'm actually pretty confused on what you argument is at this point

LMAO!!!

I give up on you, you aren't understanding.

[banditpowdercoat]

Originally Posted by Myka

Maybe I'm not being clear about what I mean, or maybe you're wrong.

We use say 1200 psi to go through a 5/8" hose then through a 1/8" fitting on the end (we use this on Hydro-Vac trucks to cut the ground), and voila! It will cut your toes off. If we use 1200 psi pumped through a 3" hose (which you would never be able to hang onto, and you'd need a muuuuuuuch bigger pump to get 1200 psi out the end of a 3" hose), and you wouldn't hurt your toes with it.

So...slap your fancy words (pressure, head pressure, velocity, psi, flow, whateeeever) on that equation, and tell me what the heck you mean that I am wrong.

But were not changing the pump. What would your 1200PSI pump out out with a open 4" hose, No nozzle. I guarantee you it wont be 1200PSI. But it still woould take your toes and whole feet off if it was exiting the hose at 1200PSI

I'm not acctually sure where this is going anymore, but head pressure is irrelavent of the volume, its height. Thats the main reason why our tank glass gets thicker the higher the tank gets. Higher water, more pressure. Regardless of vessel size. Just like pressure in the Ocean at 15ft below, is the same as in a pool at 15' below. Head pressure has nothing to do with flow or anything. Its just the weight of a column of water.

[Myka]

Originally Posted by banditpowdercoat

But were not changing the pump. What would your 1200PSI pump out out with a open 4" hose, No nozzle. I guarantee you it wont be 1200PSI. But it still woould take your toes and whole feet off if it was exiting the hose at 1200PSI

Ooooooh but that was my point!!! If it's 1200 psi out of a 1/8" nozzle, it ain't gonna be 1200 psi out of a 4" tube.

[kari]

Illustration and graph,
http://home.earthlink.net/~mmc1919/venturi.html

If it's on the internet, it must be true.

[mark]

Myka, think your need to separate pressure and flow as they are not the same thing. As for your vac truck could have a 4" line with a 1/8" nozzle and it still would probably take your toes off with the orginal pump. Reason you wouldn't have a 4" line is having to drag around the weight of the water in the hose.

[banditpowdercoat]

Originally Posted by Myka

Ooooooh but that was my point!!! If it's 1200 psi out of a 1/8" nozzle, it ain't gonna be 1200 psi out of a 4" tube.

OH. LOL I had to many beers last night

[banditpowdercoat]

But back to the basic question. Does head pressure change at the pump, when using larger diameter pipes for tank return.

NO, it remains the same. The pressure the pump see's is equivalent to the weight of water equaling the volume of a pipe the same diameter as the pump outlet, times the head height.

Now as far as friction losses, they are regardless of head height. Friction losses will happen on horizontal runs as well as vertical. If said pump was loosing flow (GPH) due to frictional losses, then yes, upping pipe size can gain back some lost GPH.

Heres a chart comparing firehose sizes and friction losses per 100' of hose. Distance and flow determine friction losses, not head height



Losses in PSI of firehose per GPM flow @ 100 PSI pump pressure

1.5" diameter
GPM/ PSI Loss

50 6.3
100 25
150 56.3

2" diameter

50 1.7
100 6.6
150 14.8
200 26.3
250 41.1
300 59.2

2.5" diameter

150 4.9
200 8.7
250 13.5
300 19.5

And for elevation, add 0.5 PSI for each foot