Grundfos DMH 25X Installation And Operating Instructions Manual page 17

5.1.3 Double-diaphragm system/diaphragm leakage detection
(optional)
General
The piston diaphragm and high-tech dosing pumps with drift-free
diaphragm leakage detection are equipped with the following:
• dosing head with PTFE double-diaphragm system
• ball non-return valve with built-in contact pressure gauge.
Double-diaphragm system
Dosing pumps with a double-diaphragm system with no diaphragm
leakage detection have no pressure gauge. In this case the ball
non-return valve is fitted with a locking unit. The valve, however,
can be retrofitted with a contact pressure gauge.
Ball non-return valve
In order for the diaphragm leakage detection to work and to protect
the diaphragms, the gap must be fully deaerated. Dosing heads
with a double diaphragm are equipped with a ball non-return valve
(T) to prevent air from flowing back during the filling and deaeration
process (2u).
6s
S
5s
3u
4u
2)
2u
U
5u
3u
T
Contact pressure gauge
Pos. Components
S Contact pressure gauge
T Ball non-return valve
U Connection piece
For dosing heads with a double diaphragm with no con-
tact pressure gauge (no diaphragm leakage detection), a
2)
locking unit is fitted instead of the contact pressure
gauge.
Functional principle of diaphragm leakage detection
The non-return valve and the gap between the diaphragms are
factory-filled with a separating agent (paraffin oil). They are set in
such a way during start-up on the test stand that there is always a
hydraulically separated equilibrium between the valve and
diaphragm gap (the pressure gauge indicates "0" when the pump is
running and when it is stopped).
If one of these diaphragms breaks, the dosing or hydraulic medium
penetrates into the gap between the diaphragms and, when the ball
is removed, into the valve. The system pressure is therefore
impinged on the valve and the contact pressure gauge is activated.
Depending on the design of the system, the electrically isolated
reed contact can trigger an alarm device or the pump can be
switched off.
The contact is triggered at the preset pressure as is shown in the
table below:
Description/use
For pumps up to 10 bar
Pressure gauge 0 to 10 bar
For pumps up to 10 bar
Explosion-proof pressure gauge 0 to 10 bar
For pumps 16 to 100 bar
Pressure gauge 0 to 100 bar
For pumps 16 to 100 bar
Explosion-proof pressure gauge 0 to 100 bar
Warning
The contact pressure gauge (Ex) in explosion-proof ver-
sion with switch amplifier should be used if the pump is fit-
ted with an explosion-proof motor.
Set pressure
[bar]
1,5
1,5
10
10
17