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Organic Water Treatment
Chemicals
Steam Boilers, Cooling Towers,
Hot And Chilled Closed Systems
Fuel Oil Treatment
(Home of D.M Concentrate)
WHY BLOW DOWN ?
The purpose of blow down is to control the amount of solids
and sludge in the boiler water. The blow down process involves
partially draining the boiler to remove sludge and to maintain
pre-determined concentration levels of solids.
As the water is turned into steam, the solids
remain behind. Unless there is 100% condensate return, the solid
content tends to build up when the boiler takes on make-up water. On
hot water systems, there is generally no make-up water. Therefore,
the solid concentration remains constant and no blow down is needed.
The amount and frequency of blow down differs for
each boiler application and should be determined by your water
management consultant. Blow down is affected by the type of boiler,
operating pressure, water treatment, and the amount and quality of
make-up water.
Blow down piping should be at least the same size as the blow down
tapping on the boiler. Blow down valves should be sized in
accordance with the ASME code and piped to a safe point of
discharge.
There should be either two slow opening valves or
one quick opening valve and one slow opening valve piped in series.
A slow opening valve is defined as needing five complete 360 degree
turns to go from fully closed to fully open. A quick opening valve
goes from fully closed to fully open in one complete motion. In the
case of one quick and one slow opening valve, the quick opening
valve should be located closest to the boiler. If possible, the blow
down valves should be piped on the same side of the boiler as the
water column gauge glass.
To blow down the boiler:
- Open the quick opening valve (valve closest to the boiler)
first.
- Open the slow opening valve last.
- Blow down the boiler for the required amount of time, per your
water management consultant, by opening and then closing the
slow opening valve. Remember: Pay close attention to the water
level in the gauge glass. Certain loads may require several blow
down cycles of short duration to maintain proper water level in
the boiler.
- Close the slow opening valve first.
- Close the quick opening valve (the valve closest to the
boiler) last.
- Open the slow opening valve again to drain the line between
the quick and slow opening valve.
- Close the slow opening valve again and double-check for tight
shutoff after the valve has cooled off.
NEVER pump the quick opening valve to blow down the boiler! This may
cause water hammer, which could damage piping and valves and may
cause personal injury. Also, NEVER leave an open blow down valve
unattended!
Remember: The quick opening valve (the valve closest to the
boiler) is opened first and closed last, which ensures its
protection from the wear associated with blow down. This will make
this valve more reliable so maintenance and repair can be performed
on the slow opening valve furthest from the boiler, without draining
the boiler.
If you have any questions regarding bottom boiler blow down,
contact your local Thermidaire representative.
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