CleaverBrooks CBLE, Operation And Maintenance Manual

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Waterside Care and Requirements
3-12 750-91 (revised 2009)
Model CB-LE Packaged Boiler Manual
When surface or continuous blowdown is not utilized, manual blowdown is used to control the dissolved or sus-
pended solids in addition to the sludge.
In practice, the valve(s) of the bottom blowdown are opened periodically in accordance with an operating schedule
and/or chemical control tests. From the standpoint of control, economy and results, frequent short blows are pre-
ferred to infrequent lengthy blows. The length and frequency of the blowdown is particularly important when the
suspended solids content of the water is high. With the use of frequent short blows a more uniform concentration
of the pressure vessel water is maintained.
In cases where the feedwater is exceptionally pure, or where there is a high percentage of return condensate, blow-
down may be employed less frequently since less sludge accumulates in the pressure vessel. When dissolved and/or
suspended solids approach or exceed predetermined limits, manual blowdown to lower the concentrations is
required.
It is generally recommended that a steam boiler be blown down at least once in every eight-hour period, but fre-
quency may vary depending upon water and operating conditions. The blowdown amounts and schedule should be
recommended by your local Cleaver-Brooks authorized representative.
A hot water boiler does not normally include openings for surface blowdown and bottom blowdown since blow-
downs are seldom practiced. The need remains to be alert to system water losses and corresponding amount of raw
water make-up. A water meter is recommended for water make-up lines.
3.8.4 — Manual Blowdown Procedure
Blowdown is most effective at a point when the generation of steam is at the lowest rate and feedwater input is also
low, thus providing a minimum dilution of the boiler water with low concentration feedwater.
1.
Be sure the blow-off piping and tank, if used, are in proper operating condition. Discharge vents should be clear
of obstruction, and the waste should be piped to a point of safe discharge.
Most blow-off lines are provided with two valves, generally a quick opening valve nearest the boiler and slow
opening globe type valve downstream. Valves will vary depending upon pressure involved and make or manu-
facturer. If seatless valves are installed, follow the manufacturer’s recommendations.
If a quick opening valve and globe type of slow opening valve are in combination, the former is normally
opened first and closed last with blow down accomplished with the globe or slow opening valve.
2.
When opening the second or downstream valve, crack it slightly to allow the lines to warm, then continue open-
ing slowly.
The length of each blow should be determined by actual water analysis. Lowering the water in the gauge glass
approximately 1/2” is often acceptable as a guide to adequate blow. However, lowering the water 1/2” should
not be interpreted as a rule since water analysis procedures should prevail. If the glass cannot be viewed by the
party operating the valve, another operator should watch the glass and direct the valve operator.
3.
Close the downstream (slow opening) valve first and as fast as possible.
4.
Close the valve next to the boiler.
Do not pump the lever action valve open and closed, as water hammer is apt to break the valve bodies or pipe fittings.
Failure to follow these instructions could cause damage to the equipment.
!
Caution