AXEON Grundfos MQ-Series - Manual (Page 21)

21
English (US)
15. 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, depend-
ing 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 but-
ton, only the flow switch is authorized to
automatically 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 overtemperature
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 potential 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, tolerances and a safety margin, we
recommend a maximum height of 50 ft
between the MQ and any tap.
4. What is the purpose of the built-in pres-
sure tank?
Answer: The built-in pressure tank comes
from the factory, pressurized at approxi-
mately 23 psi (with the pump pressure at
zero) and holds a volume of 14 ounces of
water. It is designed to minimize motor
startup due to small leaks.
5. How is the dry-run condition deter-
mined?
Answer: The dry-run alarm is declared
when the motor is running AND the flow
rate is less than 1.6 gpm AND when pres-
sure is less than the pressure switch set-
ting. When this condition lasts for 12 sec-
onds, the alarm will be declared after
1 minute, and the motor is stopped.
The MQ attempts to automatically restart
every 30 minutes for a maximum of
24 hours. If more than 24 hours pass with-
out water, the pump must be restarted man-
ually.
6. What is the maximum inlet pressure
allowed in the MQ?
Answer: For both MQ 3-35 and MQ 3-45,
the maximum 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 pres-
sure supplied to the MQ 3-45, internal pres-
sures can reach approximately 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 activate, 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. What is the priming capacity of the MQ?
Answer: Approx. 1.2 gallons.
Grundfos.book Page 21 Monday, May 23, 2011 10:17 AM