This document provides information on registered break tank design and testing procedures. It discusses the different types of registered break tanks, key components like the inlet, outlet, overflow, and float valve. It also outlines the step-by-step design procedure for sizing a break tank, including determining inlet pressure, orifice size, flow rate, overflow design, spill level, air gap, and ensuring requirements are met. Examples are provided of performing calculations to size break tanks. The registered air gap test procedure is also summarized.

1. Registered Break Tanks
Registered Air Gaps
Inlet
Outlet
Overflow
Tank
Float valve

2. Type “A” -
unobstructed
air gap
Registered Break
Tank types

3. Type “B” –
air gap with
overflow
Registered Break
Tank types

4. Type “C” –
air gap with
diverter and
overflow
Registered Break
Tank types

5. Type “D” –
air gap with
injector
NOT CURRENT
Registered Break
Tank types

6. Type “E” -
hygienic air
gap
Registered Break
Tank types

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

9. Registered Break Tank design procedure

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

12. Key terms for RBT calculations

13. INLET
ORIFICE

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.

16. Let’s have a go!
Sizing exercises

18. Table A3 – AS2845.2 : 2010 & Table 4.6.3.2 – AS3500.1 : 2018

19. 2020mm
mm

20. Table A3 – AS2845.2 : 2010 & Table 4.6.3.2 – AS3500.1 : 2018

21. 20 mm
40 mm
40 mm
75 mm
80 mm
150 mm
25 mm
25 mm
55 mm
50 mm

23. Table A1 – AS2845.2 : 2010 & Table 8.4.4.1 – AS3500.1 : 2018

24. .3 L/sec9.3L/sec

25. Fig A1 – AS2845.2 : 2010 & Fig 8.4.4.1(A) – AS3500.1 : 2018

26. 9.3L/sec9.
3 L/sec125mm125 mm
150mm150 mm

27. Table A3 – AS2845.2 : 2010 & Table 4.6.3.2 – AS3500.1 : 2018

28. 9.3 L/sec
150 m
9.3L/sec
125mm
150mm
50mm50mm

29. Table A1 – AS2845.2 : 2010 & Table 8.4.4.1 – AS3500.1 : 2018

30. 9.3L/sec
125mm
150mm
50mm
1.49L/sec

31. Fig A2 – AS2845.2 : 2010 & Fig 8.4.4.1(B) – AS3500.1 : 2018

32. 9.3 L/sec
125 mm
150 mm
50 mm
1.49 L/sec
9.3L/sec
125mm
150mm
50mm
1.49L/sec
40mm, 50mm & 75mm
200mm, 100mm & 30mm

33. A3 – AS2845.2 : 2010
4.6.3.2 – AS3500.1 : 2018

34. 9.3L/sec
125mm
150mm
50mm
1.49L/sec
40mm, 50mm & 75mm
200mm, 100mm & 30mm
40mm

35. Consolidated calculation data
Calc 1
Calc 2
Calc 3

36. Tank calc example 1
Calc data
40mm
Minimum
allowable?

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

41. Appendix “A”
NOT CURRENT