2 replies to this topic

[joonjoon]

Hi all, i have read several topics regarding the firewater jockey pump design philosophy. Would like to clarify the following:

1. Is there any code requirement that state that firewater jockey pump has to be spared? Although it is considered as a critical equipment on the facility, if the jockey pump fails in some reason, there is always firewater pump that will automatically kick in at low pressure. Therefore i would hv thought that single pump is sufficient esp if its designed to cover small leakages in the ring main.
2. We have a jockey pump onboard a FPSO which is in operation 24/7, with a manual valve installed at the min flow line discharge to maintain the ring main presdure? Is this acceptable? Or do we need to replace with back pressure regulator(15k)? I understand that most new designs hv jockey pump on start/stop basis to keep min 8barg on the ring main. The advantage with this is the saving of power. To change to this mode of operation, a separate pressure transmiter is required on the ring main which can send signal to start/stop the jockey pump. Back pressure regulator is then not required.
3. There is a minimum flow line and pump test line provided on the main fire pump discharge. Presumably the min flow line is used to protect the main fire pump. What is the pump test line for?
4. As per code, psv is required for diesel engine driven pump due to overpressure from overspeed. What could be the cause of overpressure if an additional PSV is provided on the ring main? Note that the firewater supply comes fr both forward firewater pump -primary and the existing marine fire pump electric driven.

Thanks all for taking the time to read.

[Mystified]

Hi,

 

1. Yes, single jockey pump is fine unless local regulations asks for a spare exclusively. Spare for a jockey doesn't hold any meaning at least to me. If the fire water demand exceeds jockey pump capacity to hold the pressure, main pump should kick in. As a standby pump an diesel driven pump shall always be there. Spare main pump and diesel pump may be thought of.

 

2. I think it is fine and usual practice.

 

3. Periodic testing of the fire pumps is required as per the regulations. Pumps may be idle for long times if everything is fine. It may so happen, they may actually pose problems when they are needed most. To avoid surprises, a test line is provided to facilitate periodic check without actually flowing the system. Test line discharges water to source again.

 

4. PSV is required only if the shut-off pressure with maximum suction pressure exceeds system design pressure.

 

Hope i understood your questions correctly.

[fallah]

joonjoon,

 

1-As far as I know there is no code requirement having the jockey pump to be spared; but it's normally spared with one running continuously and the spare shall be started automatically in case of fault of the first...

 

2-Minimum flow with manual valve isn't accepted. The minimum flow for such pumps is normally included a PCV directing the flow to the source tank to maintain a predetermined pressure in the fire water ring...

 

3-The pump test line is to be applied for testing the pump performance periodically...

 

4-With having the minimum flow line and all valves as CSO in pumps discharge lines, there is no possibility for pumps shut off; then no need to PSV for such overpressure on the main fire water ring...