Variomat 1 — 06.07.2016 – Rev. B English —
1 Suction pressure maintenance
– Device on the suction side of the system's circulating
pump
2 Final pressure maintenance
• Device on the discharge side of the system's
circulating pump
The "P
0
" minimum operating pressure is calculated as follows:
p
st
= h
st
/10 h
st
in metres
p
D
0.0 bar for safety temperatures ≤ 100 °C (212° F)
0.5 bar for safety temperatures = 110°C (230° F)
d
p
60 - 100 % of the differential pressure of the circulating
pump
Depending on the hydraulics
P
0
≥ p
st
+ p
D
+ 0.2 bar* (suction pressure maintenance) Enter the calculated value in the start routine of the controller, see
chapter 7.3 "Modifying the controller's start routine" on page 38 .
≥ p
st
+ p
D
+ d
p
+ 0.2 bar* (final pressure maintenance)
* Addition of 0.2 bar recommended, no addition in extreme cases
Calculation example for "P
0
" minimum operating pressure:
Heating system: Static height 18 m, run-on temperature 70 °C (158° F), safety temperature 100 °C (212° F).
Example calculation for suction pressure maintenance:
P
0
= p
st
+ p
D
+ 0.2 bar*
p
st
= h
st
/10
p
st
=18 m/10
p
st
= 1.8 bar
p
D
= 0.0 bar at a safety temperature of 100 °C (212° F)
P
0
= 1.8 bar + 0 bar + 0.2 bar
P
0
= 2.0 bar
The initial and final pressure of the following components must not overlap with the actuation pressure of the safety
valve.
• Overflow solenoid valves
• Pumps
The actuation pressure must not fall below the minimum value of the actuation pressure of the safety valve.
Note!
Avoid dropping below the minimum operating pressure. Vacuum, vaporisation and the formation of vapour bubbles are
thus
excluded.
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