Grundfos MQ Serie Notice D'installation Et D'entretien page 13

11. MQ frequently asked questions
1. What causes the MQ to start?
Answer: The MQ is equipped with both an internal
flow switch and pressure switch. Each of these can
turn the MQ on depending on water consumption.
The pump will start when:
The flow rate is greater than 0.3 gpm
OR
the pressure is below 29 psi.
2. What causes the MQ to stop?
Answer: Other than the manual on/off button,
only the flow switch is authorized to automati-
cally stop the MQ during normal operation when
flow drops below 0.3 gpm. The pump will shut off
in 12-15 seconds after flow stops.
Additionally, the MQ will be turned off in the
event of a dry-run or over temperature alarm.
3. What is the maximum height of a tap above the
MQ?
Answer: If a tap or faucet is installed at heights
greater than 50 ft above the MQ, there is the po-
tential risk that the MQ will never start. In cases
where the MQ starts due to low pressure (low flow
rates), the pressure has to fall below the pressure
switch activation point (28-30 psi factory setting).
To allow for the pressure of 50 ft of water, toler-
ances and a safety margin, we recommend a maxi-
mum height of 50 ft between the MQ and any tap.
4. What is the purpose of the built-in pressure tank?
Answer: The built-in pressure tank comes from the
factory pressurized at approximately 23 psi (with
the pump pressure at zero), and holds a volume of
5 ounces of water. It is designed to minimize mo-
tor startup due to small leaks.
5. How is the dry-run condition determined?
Answer: The dry-run alarm is declared when the
motor is running AND the flow rate is less than
0.3 gpm AND when pressure is less than the pres-
sure switch setting. When this condition lasts for
1 minute, the alarm is declared and the motor is
stopped. The MQ attempts to automatically re-
start every 30 minutes for a maximum of 24 hours.
If more than 24 hours pass without water, the
pump must be restarted manually.
6. What is the maximum inlet pressure allowed in
the MQ?
Answer: For both MQ 3-35 and MQ 3-45 the maxi-
mum internal pressure allowed is 109 psi. The
maximum inlet pressure when added to the MQ
pressure must not exceed 109 psi.
Remember that inlet pressure adds to the MQ
pressure, so with a 40 psi inlet pressure supplied
to the MQ 3-45, internal pressures can reach ap-
proximately 105 psi (65 + 40 psi).
Additionally, if inlet pressures exceed the built-in
pressure switch activation point, (28-30 psi factory
setting) the pressure switch will be unable to acti-
vate, and the ability to turn the MQ on at low flow
rates will be lost. In this situation, only the flow
switch will be able to turn the MQ on at flow rates
above its activation point of 0.3 gpm.
7. Where can a pressure gauge be easily installed?
Answer: In the ½" straight thread opening used to
add priming water to the pump.
Subject to alterations.
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