Setting The Pressure Relief Valve - Grundfos DMH 251 Installation And Operating Instructions Manual

1. Connect the electrical power supply.
2. Depending on the installation, start the pump, where possible,
without counter-pressure.
See installation example for easy deaeration of the dosing head
in section .
9. Installation
3. Set the stroke-length adjustment knob (L) to 0 %.
4. Let the pump run for approx. 5 minutes.
5. Check the oil level.
– Set the stroke-length adjustment knob (L) to 40 %.
– Let the pump run for approx. 10 minutes with a stroke-length
setting of 40 %.
– Switch off the pump, check the oil level and add oil,
if necessary.
– Refit the oil-filling screw (F).
The pump is now ready for operation.
Warning
Risk of injury caused by squirting oil!
Oil may squirt from the oil deaeration when the
pump is running. Do not completely unscrew the
oil deaeration screw.
Wear protective clothing (gloves and goggles)
when working on the dosing head, connections
or lines!
Rod length of oil dipstick: 35 mm.
Note
Immersion depth to marking: approx. 5 mm.
Check the oil level at least every two weeks and
add oil, if necessary.
Note
Only use original Grundfos Alldos gear oil!
For product number, see service instructions.
Pump type
DMH 254
DMH 254
DMH 255
DMH 255
DMH 257
DMH 257
After start-up
After initial start-up and after each time the
diaphragm is changed, tighten the dosing head
screws.
Caution
After approximately 6-10 operating hours or
two days, cross-tighten the dosing head screws
using a torque wrench.
Torques
Pump type
DMH 254
DMH 255
DMH 257

11.4 Setting the pressure relief valve

The pressure relief valve is set to the pressure given by the
customer, or to the rated pressure (maximum counter-pressure).
The opening pressure can be set to a lower value by the
customer.
26
Version Description
Single 3.5 l DHG 68
Double 4.5 l DHG 68
Single 3.5 l DHG 68
Double 4.5 l DHG 68
Single 5.5 l DHG 68
Double 7.5 l DHG 68
Torque
[Nm]
50-54
50-54
50-54
Opening pressure of the pressure relief valve
Rated pressure of the pump
[bar]
4
10
16
25
Setting the opening pressure
• To set the operating pressure, a pressure gauge must be
installed in the discharge line and an isolating valve must be
installed after the pressure gauge.
• To set the pressure relief valve, use a screwdriver.
Fig. 28 Setting the opening pressure
Set the pressure relief valve as follows:
1. Close the isolating valve after the pressure gauge.
2. Remove the cover (1m) from the pressure relief valve.
3. Start the pump.
4. Using a screwdriver, slowly turn the adjusting screw (2m) of
the pressure relief valve counter-clockwise until the desired
opening pressure is obtained.
Fig. 29 Setting the pressure relief valve
Risk of damage to the pump or system!
When blocked, the pressure relief valve does not
work properly and can produce pressures of
Caution
several hundred bar in the pump or system.
Do not block the pressure relief valve during
adjustments!
5. Replace the cover of the pressure relief valve.
6. Open the isolating valve after the pressure gauge.
Opening pressure of the
pressure relief valve
[bar]
5
13
18
28
1m
2m