Friction Loss inside the Discharge Manifold - 3" vs 4" @ 1,500 GPM
When performing some driver training last week, we did some side-by-side comparisons of different trucks concerning high volume pumping.
Both trucks were identical with one exception...
One had a 3" discharge plumbed off the side of the discharge manifold...
and the other had a 4" discharge plumbed off the top, yet still had two 90º bends in it.
Here's a pic of the 4" off the top:
You can imagine what the 3" looks like, it's identical to the 2½" facing the camera above, except it's 3".
To test the resistance, we stretched a 100' of 4" hose to a ground monitor, and screwed on a set of pitot tips used to service testing. Using a 2½" tip @ 82 psi, we were flowing 1,509 GPM. Each truck was equipped with a pressure governor to maintain constant discharge pressure, and each discharge valve was left full open (not throttled at all).
The 3" discharge had 90 psi of loss between the master gauge and the line gauge.
The 4" discharge had 30 psi of loss.
I knew there would be a difference, but not that much.
Both were Hale Qmax pumps. Hale offers a 4" off the side, without the 90º bends, but the 4" port (2433 series flange) is optional, not standard, while the 4" off the top is a standard feature on all Qmax's. The side port is known as "port P" in Hale's literature. Hale rates the 3" at 1,500 GPM, and the 4" at 2,600 GPM.
So, if you're specing out a truck, and you ever plan on pumping 1,500 GPM or more to another source through one line, abandon the 3", and embrace the 4" or larger for far less resistance.
pressure losses in pipe fittings
Actually, the picture shows three (3) 90 degree bends in the run. The first one is the turn from the manifold into the pipe and then the other two that are obvious. Pipe suppliers generally use an equivalent pipe length of 15 feet for each 90 deg. elbow, so there is an equivalent length of pipe in the engine of 45 feet plus the valve and straight piping. Using the Hazen - Williams formula the friction loss for just the elbows should be about 74 psi for the three inch at 1,000 gpm and about 18 psi for the 4 inch line. Adding in the losses for the droop snoot and the valve and your tests are right on target.