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# Pressure Drop Criteria for Pump discharge Line

## Pressure Drop Criteria for Pump discharge Line

(OP)
Input:
Fluid= ammonia at (-33 deg C)
Pump Discharge Pressure = 30 bar.
Truck tanker Working Pressure= 5 bar.

1) Pump Discharge line size is 2" and after hydraulic calculation the pressure drop is 3.5 bar/100m.
If Pump Discharge line size is 3" and after hydraulic calculation the pressure drop is 1.5 bar/100m.
2) Control valve is provided at discharge line

Question:

At 2" line size pressure drop criteria is not following, Do we have to increase the line size????? But since the working pressure of destination equipment is very low compare to pump discharge pressure and the rest pressure drop will be taken care by the control valve, Can we consider this line size????

At 3" line size pressure drop criteria is nearly following but meanwhile the cost is increasing. Here also we have to drop the pressure till destination equipment working pressure!!!!!!! Owner does not want to increase the line size.

Give me your Opinion in this topic

With Regards

### RE: Pressure Drop Criteria for Pump discharge Line

OK, Lots of missing data, but let's go with:

Pump has discharge of 30 bar at your flow rate (unknown)

Length of your 2" line is?? lets say less than 500m

Your pressure drop criteria is ?? your velocity is ?? What is the issue over pressure drop criteria??

Anyway lets assume that for a 2" line your arrival pressure at the end of the line is 10 bar or greater and the remaining pressure is then lost across the control valve before it enters the truck.

Can you use 2" - Possibly - depends on your velocity and any limits associated with that, any issues over surge pressures from sudden valve closure ( much worse when operating above 2.5-3m/sec). You are using a pump which has an outlet pressure which is too high for your use so you are wasting energy, but maybe the operation doesn't happen very often or you can't change this.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Pressure Drop Criteria for Pump discharge Line

(OP)
To,
LittleInch (Petroleum)

Flow rate= 34m3/hr
density= 681kg/m3

This hydraulic calculaton is at initial stage, so we have to calculate pressure drop at 100m only.

Pressure drop criteria for Pump discharge line is 1bar/100m. velocity is 5m/sec.

At last sentence you said i can use 2" line right??? thats mean here we can ignore the criteria, here velocity is 5m/sec and this comes under criteria. And yes the operation does not happen often....

(Regarding velocity criteria which you have mentioned that it should not go beyond 3m/s, I've also read this but owner is ok with 5m/s)

With Regards
Navneet

### RE: Pressure Drop Criteria for Pump discharge Line

Can you use it - yes,

Should you use it - up to you and the client providing you're checked it against design criteria. Where it doesn't meet the criteria, then note it as an exception and check

erosion: - shouldn't be a big issue
surge / water hammer - you need to check
pressure rating of system and reliefs for pressure regulating system

If this is an occasional use system I can't see any real issues operating at 5m/sec, but I'm not familiar with ammonia.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Pressure Drop Criteria for Pump discharge Line

And not to mention where does the operating point for the pump fall on its operating curve?
Will this be destroying the pump?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

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