Grundfos DMH 25 Serie Montage- Und Betriebsanleitung Seite 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).
S
5s
4u
U
5u
T
Fig. 7 Contact pressure gauge
Pos. Components
S Contact pressure gauge
T Ball non-return valve
U Connection piece
2) For dosing heads with a double diaphragm with no contact
pressure gauge (no diaphragm leakage detection), a locking
unit is fitted instead of the contact pressure gauge.
6s
3u
2)
2u
3u
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
version with switch amplifier should be used if the
pump is fitted with an explosion-proof motor.
Set pressure
[bar]
1.5
1.5
10
10
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