7. Registered Break Tank design procedure
Work out inlet pressure in kPa
Determine orifice size in mm (not just the valve size)
Use appropriate table to select the appropriate incoming flow in L/sec
Table 8.4.4.1 – AS3500.1 : 2018 or Table A1 – AS2845.2 : 2010
Determine the design of the overflow outlet
Figure 8.4.4.1(A, B or C) – AS3500.1 : 2018 or Figure A1, A2 or A3 –
AS2845.2 : 2010
Choose from the table a combination of spill level distances and
overflow sizes that meet the requirements of the specific tank location.
8. Registered Break Tank design procedure
Continued
Note the chosen spill level distance in mm.
Determine whether the inlet discharge point is affected by near wall
Use appropriate table to select the appropriate air gap in mm.
Table 4.6.3.2 – AS3500.1 : 2018 or Table A3 – AS2845.2 : 2010
Add the air gap measurement and the spill level distance together to
provide you with the minimum distance between the discharge point of
the inlet float/servo valve and the invert or weir of the overflow pipe
10. Air Gap Requirements
For a Registered break tank to be considered as a backflow
prevention device for high hazards, it must maintain an air gap
AT ALL TIMES.
11. Air Gap Requirements
The position of the inlet valve discharge point in relation to the invert of the overflow pipe will dictate if
the air gap requirements are being met.
There are a number of factors that will affect the above positions;
1. Inlet pressure to the tank in kPa
2. Orifice size on the float /servo valve in mm
3. Flow rate into tank in L/sec
4. Design and location of overflow outlet
5. Size of overflow outlet in mm
6. Spill level in mm
7. Position of inlet discharge point
8. Air gap in mm
14. The Near Wall
Air gap is affected when the distance from the tank wall to the control valve
outlet is less than 3 times the effective opening – single wall.
15. The Near Wall
4 times the effective opening
Float valve
Effective opening
4 times the effective opening from two
intersecting tank walls
Air gap is affected when the distance from the tank wall to the control valve outlet is less
than 4 times the effective opening – intersecting wall.
37. Tank calc example 2
Calc data
10mm inlet orifice
40mm
Fred Bloggs Tanks
Cert:Joe Smith
(Joe’s Plumbing)
38. Tank calc example 3
Calc data
32mm float valve
150mm
?
?
Fred Bloggs Tanks
Cert:Joe Smith
(Joe’s Plumbing)
39. RAG Test procedure
a) Measure and record the distance from the spill level to the
outlet of the water service
b) Check the air gap complies with Table A3 (Minimum air gap),
Appendix A of AS2845.2
40. RBT Test procedure
a) Check that the break tank has an overflow fitted below the level of the inlet
b) Inspect overflow for any obstructions
c) Check that there is no bridging device between the outlet and the water in the
tank
d) Record the size of the inlet orifice and calculate cross-sectional area for the
overflow
e) Measure and record the height (h) of water above the invert of the overflow, in
millimetres. Height (h) shall comply with the requirements of AS2845.2