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Dear all,
I am calling your opinions about the problem on the wet sprinkler system at down stream an alarm check valve of a firewater system
I have a firewater system including 2 jockey pumps without any PSV or PCV at downstream discharge line and 2 Diesel firewater pump with PSVs @discharge set at 11.2 barg (and no PCV).
Normal operating pressure of ring main is 10barg, when it drops to 9barg, Jockey pump to start. If pressure drop continuously to 7barg, first firewater pump starts, and still drop to 6barg, 2nd firewater to start. Design Pressure of system is 12barg.
The ring main distributes to 3 distinct wet sprinkler systems via three Alarm check valves provided by Viking J1 model.
In theory, if the system is under normal operating condition, the pressure on the ring main is maintained at 10barg and roughly 10 -11barg after alarm check valve.
However, the issue happened to this system is when Jockey pump start, it generates around 14barg -16barg in about 10 seconds measured at PG @just upstream of Alarm check valve, this (high) pressure pushes to open Clapper and also goes through an external bypass of this check valve to increase pressure the system at downstream alarm check valve to above 12barg. When the firewater pump starts (based on our trial test at site), it can bring the pressure of downstream alarm check valve system to 14barg (higher design pressure).
(As per NFPA 13, on the closed wet system, it should have an air reservoir or TSV to avoid thermal expansion. Air reservoirs provided but they haven't installed yet).
Refer to Alarm check valve operating and manual, the chamber attached with the valve is designed to absorb any surge from supply system, but it seems it doesn't help in this case.
Based on several tests at site to ensure Alarm check valves and firewater control system work correctly, we found that pump control system work fine, no such high pressure recorded at PG @pump discharge, therefore, we concluded that this is due to surge problem.
Some ideas are proposed to solve this problem as:
1. Request firewater pump vendor to limit the maximum head that pump motor can generate. (we are contacting vendor but no response yet)
2. Install TSVs (set at 12 barg) on wet Sprinkler system to release this exceed pressure (in my opinion, this is lacking NFPA 13 because this TSVs are for thermal expansion and the pressure of this system increase due to surge pressure).
3. install an anti-surge pump control valve.
4. install a PSV (3/4" x 1") on Jockey pump discharge (I doubt this option because the surge time is only few seconds)
Drawings and sketch of alarm check valve is attached for reference.
I found a surge on fire water system topic in this forum but it doesn't help me on this matter.
If anyone of you faced a similar matter before, please advise me your idea. I do appreciate any advice and opinion.
Thanks in advance.
Linda,
