Choosing Piping Size

[Toyoranger]

I am in charge of a project where we are upgrading a wash system for the automotive industry. We are using a Goulds 92SV pump. Specs for the pump as are follows;

Flow at Design: 390 USGPM
Head at Design: 519 FT.

The basic premise of this is that water is pumped to 3 headers measuring 48" in length with 13 nozzles each. Each header must be supplied with 130 GPM. The water pressure exiting the spray nozzle must be at least 200 PSI. The male pipe connection on the nozzle is 1/4" NPT with an equivalent orifice diameter of .149 inches.

I am having difficulty in determining the pipe size for the headers themselve. I just need a rough pipe size for this application as the company that this is being supplied to is going to run the pipping from the pump to the headers. The total distance the pump is going to be is under 5 ft.

If anyone has just a basic way to get a rough size for the piping it would be much appreciated.

 

[zdas04]

You can afford about 20 psi dP from the pump discharge to the nozzles, but with piping that short, I'd plan on 5 psi dP. Use the Hazen-Williams equation to get to a pipe size that gives you 5 psi dP at your 390 gpm.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[Toyoranger]

Attached is a rough visual of what it is going to be.

 

[Latexman]

A refresher on "flow distribution" and/or "maldistribution" may do you good. Use Search, under the thread title and between Forum and FAQs.

Basically, to get good distribution (or little maldistribution), the dP of the spray nozzles (200 psi) must be large compared to the dP of the headers (main pipe - 390 gpm) and sub-headers (single pipe - 130 gpm).

So, you need pipe sizes so dP << 200 psi. For 4-5 feet of pipe, that should be easy. Just choose a calculation method and have at it. zdas04 suggested the Hazen-Williams equation. That's a good one for water. There's also some look-up tables in Crane Technical Paper No. 410, the Cameron Hydraulic Data manual, and about a hundred other places.

Just don't use so much pressure drop in 4-5 feet of pipe that you have erosion problems though (too high of a velocity). Design for reasonable velocities, say < 15 ft/sec.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[Toyoranger]

Thanks for the guidance. I definitely need to do some brushing up on my fluid dynamics. After going through some calculations and looking through some charts. It appears that 2" schedule 40 piping will work best for the headers in this situation.

Thanks again.

 

[Latexman]

Not to be picky, but in my terminology above, "It appears that 2" schedule 40 piping will work best for the" sub-headers "in this situation". The main header feeding the three sub-headers needs to be larger than 2" for < 15 ft/sec.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[bimr]

Water velocities for general purpose use should be between 3-10 ft/sec.

Use an online calculator:

http://irrigation.wsu.edu/Content/Calculators/General/Pipe-Velocity.php

That would give you 4-Inch for the header pipe and 3-Inch for the three laterals.

 

[racookpe1978]

For this application, his weight of the piping header AND the three distribution pipes is going to be a substantial weight (empty and full) that have to move (sprayed at cars, so absolutely no contact with the car body, right?) and that need to absorb the water reaction force from the three nozzles.

Going to be a pretty substantial power supply and actuator arm.

 

[Latexman]

I was thinking it was car parts on a production line/conveyor belt going through a degreasing/wash station, so the water spray system is fixed and not moving. The header and sub-headers are only 4-5 feet in length, so it can't be that big. Toyoranger, what is it?

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[Toyoranger]

It is a high pressure wash system for the masks used on automotive lenses. The masks are nickle electroforms that cover either painted, clear or metatllized parts of the lens from the next process on the production line. Periodically these masks must be remove and cleaned. This is where the mask washer comers into play. They are set into it vertically on a rotator and spins while it is pressure washed. You can go to

http://www.met-l-tec.com

to see what this is used for.