Setting The Pressure Relief Valve; Zero Point Adjustments (Dmh 281-288) - Grundfos DMH 28 Serie Montage- Und Betriebsanleitung

8.4 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.
Opening pressure of the pressure relief valve
Rated pressure of the pump
[bar]
50
100
200
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 for DMH 280.
– use a special tool for DMH 281-288.
Fig. 29 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. Adjust the pressure relief valve.
– DMH 280: Using a screwdriver, slowly turn the adjusting
screw (2m) of the pressure relief valve clockwise until the
desired opening pressure is obtained.
– DMH 281-288: Using the special tool, slowly turn the
adjusting nut (2m) of the pressure relief valve clockwise until
the desired opening pressure is obtained.
Fig. 30 Setting the pressure relief valve
28
Opening pressure of the
pressure relief valve
[bar]
55
110
210
1m
2m
Risk of damage to the pump or system!
When blocked, the pressure relief valve does not
work properly and can produce pressures of several
Caution
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.

8.5 Zero point adjustments (DMH 281-288)

8.5.1 Adjusting the zero point for system pressures up to 100
bar
The zero point of the dosing pump is factory-set to a slightly lower
counter-pressure than the rated pressure of the pump. If the
operating counter-pressure deviates considerably from this value,
an adjustment of the zero point will ensure more precise values.
Counter-pressure at the factory-set zero point of the pump
Rated pressure of the pump
[bar]
50
100
8.5.2 Adjusting the zero point for system pressures of 100
bar and up
The pump cannot run if the stroke-length adjustment
knob is fully open. Depending on the pump
Caution
adjustment, this value may already be lower than 100
% on the scale for system pressures of 100 bar and
up.
Adjusting range approx. 20-100 %
If the rated pressure of the pump is 100 bar or higher, the maximum
dosing flow is factory-adjusted to a scale value of 100 %. The zero
point is not set. The zero dosing flow is reached depending on the
system pressure, e.g. already at 20 % on the scale.
Adjusting range approx. 0-80 %
You can make an adjustment so that the zero dosing flow is at a
scale value of zero, but the non-permissible operating range is
then within the 100 % of the scale value! Loosen the
stroke-length adjustment knob completely for a maximum dosing
flow, and then close it by approx. 10 %.
Counter-pressure at the factory-set zero point of the pump
Rated pressure of the pump
[bar]
200
Counter-pressure at the
factory-set zero point
[bar]
30
80
Counter-pressure at the
factory-set maximum point
[bar]
160