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Testing gauge glass and water column,Precautions to be taken when blowing down a boiler.



Q. Testing gauge glass and water column:

A. (See diagram) To determine whether the pipes and terminal cocks are clear a blowing procedure sometimes referred to as cross blowing is adopted. First do the column.

 

(1)   Cocks A, C and D open, cocks B and E closed, this checks that A, pipe X and the column are clear.

(2)   Then with cocks E, B and D open, cocks A and C closed, checks that E and pipe Y are clear.


Next, blow the water gauge glass with A and E open.
(1)   Close steam (B) and water cocks (C) then open the drain (D).  Nothing should blow out of the gauge if the steam and water cocks are not leaking.
(2)
   Open and close water cock (C) to check that the water cock connection to the boiler is clear.
(3)
   Open and close steam cock (B) to check that the steam cock connection to the boiler is clear.
(4)
   Close the drain (D).
(5)
   Open the water cock (C).  Water should then gradually rise up to the top of the gauge glass.
(6)
   Open the steam cock (B) and the water in the glass should fall to the level of the water in the boiler.

- If when (5) is reached the water cock is opened and water does not flow up the gauge glass, the water level in the boiler is below the water cock connection to the boiler and it is unsafe to put feed water into the boiler.
- If when the water cock has been opened the water flows to the top of the gauge glass and then when the steam cock is opened the water flows down and out of the glass, the water level is between the water cock connection to the boiler and the bottom of the gauge glass.  In this case it is safe to put feed water into the boiler.
- If after (5) when the glass is full of water, the steam cock is opened and the water in the glass does not descend in the glass, the water level is above the steam cock connection to the boiler and there is a danger of priming the boiler if any additional feed is put into it.

Q. Precautions to be taken when blowing down a boiler.A. A modern boiler should never be blown down while the boiler is steaming at high rates. To blow down...Cut the fires and close the steam and feeds stops. Allow the boiler to cool off. At 25psi,  blow down to sea, the shipside valve should be open first, then the blow down valve. This will maintain control to the operator should a pipe burst.
Care must be taken that no cold sea water enters the boiler due to residual steam cooling to create a vacuum. A non return valve would prevent this from happening but prudence would dictate shutting off blow down valve when getting close to no pressure.
Open boiler vent to allow as much natural cooling as possible at atmospheric pressure. Remove belly plug to drain the remainder contents in the bilge.
One door can then be open, top or bottom, but not both and with care. Loosening dogs, but not undoing then to determine condition on other side… steam, hot water. Once determine door can be open being careful of remaining hot water.

Q. What are the dangers in relighting a boiler. A. Obvious precaution should be taken before lighting. These include, making sure all doors are closed and gas passages are open, and there is water in the boiler. Un-burnt fuel and vapors exist in the boiler, these may lead to an explosive atmosphere. To prevent this, carry out a visual inspection of the furnace, followed by purging by forced draught with all air registers open for several minutes.

Q. Precaution to take to prevent backing one boiler into another. A. Non return / check valves, manual monitoring, flow meters / alarm. Isolating boiler operation and blow downs.

Q. Precautions to take when connecting one boiler to another. A. The objective is to minimize dangerous thermal shock. And stresses. The connecting steam pipe must have drain open, and be gradually preheated by cracking the steam valve slightly. Once pressure is about 90% of one another, the steam stop valve can then be open.


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