piping calculation

Hello,
I have to calculate the size of a collecter-manifold.
The outlets (2 inch each) of the cooling systems of six diesel engines (drivers for 6 fire fighting pumps) should be collected onto a collecter in order to be driven back to a water tank.
What is the proper diameter of the collecter? Practically the diameter is depended on the flows only or not?
cheers

 

[pardal]

Hi
questions:
1.- the flow involved?
2.- the pressure drop allowed?
3.- Did you have any specs to complain.?
4.- how many pumps will run at once?

 

[TD2K]

Ultimately, you will need to check the hydraulics through the cooling loop to ensure that the backpressure exerted by your collection system is within the capacity of whatever pumps you are using to ensure circulation of cooling medium through the firewater pumps' drivers. This doesn't have to be a detailed model, the complexity and accuracy of your calculations depends how much pressure drop you can take over the collection piping versus what is available.

If the piping is 'short', then very likely the collection manifold will be sized on a maximum velocity. As suggested, you need to consider how many pumps can be running at once (is one of the FW pumps a dedicated backup spare for mtce?) and then size the collection manifold for no more than perhaps 13 to 15 feet/sec. Caution, you are going to have some significant line losses at this velocity hence my comment about checking the hydraulics (in a 4" line at 15 ft/sec or about 600 gpm, you will have about 8 psi per 100' piping) . Once you know the maximum water flow rate and the overall hydraulics, it's a brief exercise to determine the correct size. You can always go up one pipe size for not much additional cost (and much less dP).

 

[peterpom]

Hi Elpa,

Rule of thumb, 6 x 2" pipes equals 1 X 5" (well slightly less actually, so 5" kills it) However, you may find 6" easier to buy.

Alternatively, if budget or space are a problem, you need to get ALL the info, and engineer it properly. The most important bit of info, is do all the engines run at once? If not, you can reduce the size accordingly.