# Thread: Pump Hydraulics Question

1. ## Pump Hydraulics Question

Good Evening...

I was asked a question tonight that I am having difficulty figuring out. The question was...

" we are in the process of specing a new 1050gpm pumper. We want a 4in stortz discharge, but we want to know the difference in volume if the pipe from the pump is 3in or 4in. (note this is separate from the 6in to 4in steamer port) The difference in price is a lot."

So, I need to know the difference in volume of a 4ft 3in pipe to the stortz 4in and 4ft 4in pipe to a stortz 4in. Pumping at 100psi
Confused>?

Thanks.

Firebuzz.

2. Im at home so I dont have my flow charts and we dont have anything 4" so I dont know it off hand. I would guess all you need to know is the flow for 3" and the flow for 4" @ 100psi. I wouldnt think it would matter much with only a 4' pipe, or that your going 3" into 4" as opposed to reducing size (ie 3" to 2 1/2"). Perhaps you should contact the pump builder.

3. The friction loss for pipe only goes up to 500 GPM (US) for 3" and 4" pipe (with the chart I have). The friction loss for flowing 500 GPM through 4' of 3" pipe is 1.232 psi and the loss of 500 GPM through 4' of 4" pipe is .2972 psi or a difference of .9348 psi.

If we use the friction loss for hose which is less than pipe for 1000 GPM flow we can calculate the friction loss and the difference. Friction loss through 4' of 3" hose flowing 1000 GPM is 3.06 PSI and the loss of 1000 GPM through 4' of 4" hose is .76 psi or a difference of 2.3 psi.

As you can see there is not a tremendous difference. I would use the same reasoning for why I do not need a 4" valve and am fine with a 3.5" valve.

4. ## A suggestion...

Can I make a suggestion...and I'm not trying to be a smartass...

Spec the rig based on what you want the LDH discharges and the intakes to be able to flow or draft and let the manufacturer determine the piping needed to meet your specifications. Our engine was done that way...the 2,000 gpm two-stage pump was spec'ed by us, but the intakes and discharges were spec'ed based upon performance, not on physical characteristics.

Some examples:

- We spec'ed a front intake/discharge which could draft or discharge a minimum of 1,000 gpm (it exceeds both)

- We spec'ed a passenger-side intake which can draft the full 2,000 gpm...Pierce came up with a mounted dual 6" "pants leg" style suction siamese (I know for a fact that you can draft at least 1,985 gpm through it, because I did that very number with it during a drill a few months ago)

The key to this is to make the manufacturer show you the results on your approval visit and make them re-work the rig if they can't show you the results (this wasn't a problem for Pierce).

Just a suggestion...

5. I completely agree with bobsynder - Make a performance based specification and let the builder figure it out.

Our 1,500 gpm pumper has two 3" valves (connected to one handle) siamesed into a 4" pipe. All of the this is hidden behind the pump panel.

6. I agree with the performance spec idea.

Also note that most likely your 3" discharge will provide all the flow you need/can generate. I recently flow tested a 2 1/2 discharge on the rear of a pumper that flowed 700gpm into a 4" w/o driving the pump all that hard. That pipe had to be at least 15 feet long. The purchaser of the truck spec'd that the pipe must flow 700gpm, the engineers said 2.5" was OK, and it was.

7. First, I agree with writing a performance specification. The spec must include a clause that a condition of acceptance is a test of the performance spec.

To answer the original question (as I interpret it) the difference in volume (I believe you mean flow rate) is a factor of approximately 2 for the same friction loss. The flow rate through a 4" pipe is approximately 2 times the flow rate in a 3" pipe (Schedule 40 or 10) given the same friction loss.

For example, 1,098 gpm flowing through a 3" Schedule 40 pipe 4.33 ft long creates approximately 5 psi pressure loss. 2,245 gpm through a 4" Schedule 40 pipe 4.33 ft long creates a pressure loss of approximately 5 psi. It doesn't matter what the pressure is (100 psi in your case), the ratio of the flow rates is independent of the pressure.

You say the price difference is "a lot". Please, what is "a lot"? I am curious.

Finally, have you considered 5" stortz? Why not go for a 1,500 gpm pump? I am thinking of the future as well as getting more flexibility now. For example, the 1,050 pump will pump 1,050 gpm at 150 psi while the 1,500 gpm pump will pump 1,050 gpm at 200 psi. If you do any relay pumping this can have an advantage. You will get an extra 600 feet of 5" hose for the extra 50 psi (at 1,000 gpm), probably more depending on the hose manufacturer.

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