Answer MEP Question 9
Q. Explain in detail how you would isolate one of the sprinkler systems for routine maintenance. Describe all tests and inspections you would make and how you would return the system to service.
Sprinkler system:-
The structural fire protection is based on zones separated by a fireproof bulkhead and having fireproof divisions within them. A network of sprinklers head is arranged throughout the spaces to be protected each sprinkler head is normally kept closed by a Quartziod bulb which is almost filled with a liquid having a high expansion ratio.
When liquid is exposed to abnormal heat it expands rapidly to completely fill the bulb, further, expansion is sufficient to shatter the bulb. Water maintained under pressure by compressed air is then expelled from the sprinkler head or heads in the form of a heavy spray. Each head adequately showers a deck area of 16meter square and the heads are arranged so that every part of each space requiring protection, can be covered by water spray.
The system has a pressure tank which is kept part filled with fresh water and pressurized to 8Bar by compressed air when the pressure drops below 5.5bar, a saltwater pump cuts in automatically so that if the sprinkler operates a supply of water is maintained.
Each installation is divided into sections containing up to 200 sprinkler heads and each section has an alarm valve. When a sprinkler comes into operation, water flows through the section alarm valve. The water lifts the N/R- valve exposing an annular groove that connects to a diaphragm alarm switch. This switch is coupled to an alarm valve and to an indicator panel on the bridge which gives an audible and visual warning that a sprinkler has operated and fire has probably broken out in the section indicated. Fire have frequently been found to have been extinguished by the system alone. When any occurrence has been dealt with, the stop valve which is usually locked open may be closed to replace the sprinkler head which has operated and to enable the section to be drained of saltwater before filling with fresh water.
Any maintenance on a section is carried out with the stop valve closed. Inform the bridge about the intended job and time out outage and expected time of job completion.
The test valve can be opened to create flow and cause the N/R section alarm valve to open, to test the alarm. The alarm from this section is disabled from the local location or from the bridge.
Disable the seawater auto-start to avoid the pump starting in the event of a pressure drop. The section drain valve is opened for draining which drains into the scupper.
Regular maintenance of the system consists of greasing the various valves and checking their freedom of movement, logging the pressure gauge reading, before and after each alarm valve (Thus checking the tightness of the non-return valve) and checking the alarm system. The latter is done by opening the test valves and checking that the audible and visual alarms work. The pressure tank level is checked and recharged; if necessary, with fresh water and air. The centrifugal saltwater pump should also be tested by closing the isolating valve and draining the pressure switch circuit. When the pump starts automatically the delivery pressure should be logged. In the event of a fire, when a normal situation is recovered the section and system are drained and flushed out; then recharged with fresh water and air.
Isolation:-
Sprinkler system:-
The structural fire protection is based on zones separated by a fireproof bulkhead and having fireproof divisions within them. A network of sprinklers head is arranged throughout the spaces to be protected each sprinkler head is normally kept closed by a Quartziod bulb which is almost filled with a liquid having a high expansion ratio.
When liquid is exposed to abnormal heat it expands rapidly to completely fill the bulb, further, expansion is sufficient to shatter the bulb. Water maintained under pressure by compressed air is then expelled from the sprinkler head or heads in the form of a heavy spray. Each head adequately showers a deck area of 16meter square and the heads are arranged so that every part of each space requiring protection, can be covered by water spray.
The system has a pressure tank which is kept part filled with fresh water and pressurized to 8Bar by compressed air when the pressure drops below 5.5bar, a saltwater pump cuts in automatically so that if the sprinkler operates a supply of water is maintained.
Each installation is divided into sections containing up to 200 sprinkler heads and each section has an alarm valve. When a sprinkler comes into operation, water flows through the section alarm valve. The water lifts the N/R- valve exposing an annular groove that connects to a diaphragm alarm switch. This switch is coupled to an alarm valve and to an indicator panel on the bridge which gives an audible and visual warning that a sprinkler has operated and fire has probably broken out in the section indicated. Fire have frequently been found to have been extinguished by the system alone. When any occurrence has been dealt with, the stop valve which is usually locked open may be closed to replace the sprinkler head which has operated and to enable the section to be drained of saltwater before filling with fresh water.
Any maintenance on a section is carried out with the stop valve closed. Inform the bridge about the intended job and time out outage and expected time of job completion.
The test valve can be opened to create flow and cause the N/R section alarm valve to open, to test the alarm. The alarm from this section is disabled from the local location or from the bridge.
Disable the seawater auto-start to avoid the pump starting in the event of a pressure drop. The section drain valve is opened for draining which drains into the scupper.
Regular maintenance of the system consists of greasing the various valves and checking their freedom of movement, logging the pressure gauge reading, before and after each alarm valve (Thus checking the tightness of the non-return valve) and checking the alarm system. The latter is done by opening the test valves and checking that the audible and visual alarms work. The pressure tank level is checked and recharged; if necessary, with fresh water and air. The centrifugal saltwater pump should also be tested by closing the isolating valve and draining the pressure switch circuit. When the pump starts automatically the delivery pressure should be logged. In the event of a fire, when a normal situation is recovered the section and system are drained and flushed out; then recharged with fresh water and air.
Isolation:-
- To isolate any section the bridge has to be informed about the intended job, time out outage and expected time of job completion.
- Close the main sectional valve (stop valve).
- The alarm from this section is disabled from a local location or from the bridge.
- The seawater pump auto start has to be disabled.
- The section drain valve may be opened for draining which drains into the scupper.
Maintenance:-
Maintenance:-
- Top up fresh water and air.
- Greasing and logging gauge readings.
- Checking the alarm system by opening the test valve and checking that the audible and visual alarm working.
- Seawater pump was tested by closing the isolation valve and draining the pressure switch circuit. The pump should start automatically.
- Each sprinkler head should be checked regularly for any sign of a leak, corrosion of the connector, any salt deposition.
- Check and ensure the appropriate bulb is fitted to different temperature zones.
- Check alarm for individual section. An indication should be checked i.e which section has operated.
- Check the isolation valve for each section for operation and indication.
Return back:-
Return back:-
- Refill and pressurize the isolated section, first the drain is still left open and the section isolation valve is cracked open and some water is drained to flush the system out.
- Close the drain and slowly start to fill the section.
- This will cause the tank level to fall. The tank is to replenish to the required level only after the stop valve is fully opened.
- Press up the tank with air up to 8-8.5 Bar.
- Put seawater pump back to auto mode.
- Put alarm to Normal
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