No replies to this topic

[mykid]

Hi all,

I have few questions with regards to the design of the firewater system.

I have seen a few offshore installation with diesel driven firewater booster pump with hydraulic driven seawater lift pump.

 

Some of them has a PSV installed at the pump discharge, while some has a pump minimum flow line and a separate test line. I have gone through NFPA as well as ABS SVR, the following is my understanding, please correct me if it's wrong:

 

1. For diesel engine driven firewater pump, PSV is required only if engine overspeed is possible to cause overpressure beyond the piping design pressure.

 

2. No minimum flow is required for engine driven firewater pump if the engine cooling is taken from the pump discharge. If it is electric driven, then minimum flow line is required for pump protection.

 

3. A separate firewater test line is required for firewater pump testing. A flow meter is not mandatory.

 

For wet firewater ring main, firewater pump will be started when the ring main pressure drops below PALL ie. 2.5 barg. An air release valve is provided at the booster pump suction to ensure all the air trap in the suction piping will be vented off before the ring main. However how do we determine if surge will occur during firewater pump start?

 

For dry firewater ring main, the minimum requirement is to for the seawater to reach the farthest user within 30 seconds after pump start.

 

I am thinking to remove a minimum flow line from the firewater pump discharge since there will be continuous seawater for engine cooling during pump start. The current minimum flow is maintained with a self regulating PCV. The set pressure is wrongly put at 150% flow for some reason. I am not sure if the PCV is meant for minimum or surge control.