Boiler house Blowdown vessels
2
Table 1 Equivalent straight lengths Blowdown line size 25 mm (1") 32 mm (1 ¼ ") 40 mm (1 ½ ")
Table 3 Vent head selection Note: The vent head required depends on the vessel selected
50 mm (2")
For a BDV60/3 select a VH4 vent head For a BDV60/4 select a VH4 vent head For a BDV60/5 select a VH6 vent head For a BDV60/6 select a VH6 vent head For a BDV60/8 select a VH8 vent head For a BDV60/10 select a VH8 vent head
Pipe fitting or valve
Equivalent length in metres
Long radius bend
0.5
0.7
0.8
0.9
Manifold inlet
1.1
1.5
1.7
2.2
Globe valve
9.6
12.2 13.9
17.8
Check valve
3.6
4.3
5.0
6.3
Blowdown valve
0.3
0.4
0.4
0.5
Graph 1 Blowdown flowrates This graph will give the flowrate of blowdown in litres per second. When this value has been read, multiply it by the duration of blowdown (seconds), and the answer will be the maximum volume discharged.
Table 2 Blowdown vessel selection Blowdown line size 25 mm (1") 32 mm (1 ¼ ") 40 mm (1 ½ ")
2.9 5
50 mm (2")
Blowdown line size
Boiler pressure bar g psi g 5.5 80
Blowdown vessel BDV60/_
3
3
3
4
7.6
110
3
3
4
5
8.3
120
3
4
4
6
10.3
150
3
4
5
6
12.1
175
4
4
5
8
17.2
250 300 350 400
4
5
6
8
20.7
5
6
8
10
24.1
5
6
8
10
27.6
6
8
8
-
Note: For intermediate pressures go to the next higher pressure.
Boiler pressure (bar g)
How to select the blowdown vessel: Step 1. With the aid of Table 1 , determine the equivalent straight length of the blowdown line. Step 2. Use Table 2 to initially establish the correct size of vessel. Note that if the result of Step 1 is less than 7 m, multiple the boiler pressure by 1.15. If the vessel is to be used in the conditions set out above, then continue to Step 4. Step 3. Using Table 4 which contains the vessel data, establish the volume of standing water in the selected vessel. This volume should be at least twice that of the maximum volume of blowdown. The maximum volume of blowdown is usually the volume discharged when blowing down from 1st low level to 2nd low level alarm. If this volume is unknown, it can be calculated with the aid of Graph 1 , where details on its use are given. If it is determined that the volume of standing water is insufficient, then a larger blowdown vessel must be selected in order to satisfy this requirement. Step 4 . With the aid of Table 3 , the correct vent head can be selected to suit the vessel.
The selection is now complete. Selection example: For a 10 bar g boiler with 40 mm blowdown line at least 7 m long select, from Table 2 , a BDV60/5 . From Table 3 select a VH6 vent head.
TI-P405-33 EMM Issue 9
Page 5 of 7
BDV60 Blowdown Vessels
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