19
CALCULATION EXAMPLE
Example of a calculation for a CHX 21-1000 pump installed at 500 m above sea level
The calculation shows that the pump can suck from a height of 1.98 m (6.53 ft). If the Hz
value is positive, the pump should be supplied under the head of water
.
5.2 D) Protection against overheating
Besides reducing the life of the gaskets, operation with very hot water can cause cavitation
and must be avoided.
Reduced rotational speed of the motor.
If the pump is connected to an electric motor controlled by a speed converter, it is
worthwhile installing a device that reduces the rotational speed of the motor and,
consequently, the pump flow rate, when the bypass valve is operating. This ensures
that the water does not heat so much.
A
thermostat
installed in the tank that trips when the water becomes too hot or,
when possible, stops the pump motor, is another recommended safety system.
5.2 E) Protection against insufficient or no water supply
The pump must never operate dry, since this would lead to abnormal wear on the gaskets
and cause overheating, which could break the pistons or irreparably damage the pump
itself.
A
level switch
that signals when there is insufficient water in the tank or, when possible,
that stops the pump motor, is recommended for the purpose of preventing the pump from
running dry.
A
pressure switch
, which trips with an alarm signal or, if possible, which stops the motor
when the supply pressure drops below the value liable to cause cavitation, should be
installed upstream of the pump suction duct.
If the level switch, thermostat or pressure switch trip and stop the motor, the switch
used must be the manual starting type to prevent the motor from restarting on its
own.
5.2 F) Energy saving / correct use of the pump
It is fairly frequent for the flow rate of the pump to be oversized with respect to the effective
requirements.
To correctly size the system, the water re-circulated through the regulating valve must not
exceed 10-15% of the pump flow rate.
Length of pipes (drawing)
1+1+2=
4.00 m
3.3+6.6+3.3= 13.20 ft
Equivalent length
2X1.31=
2.62 m
of unions (tab.2)
2X4.31=
8.62 ft
Total length
6.62 m
21.82 ft
H1 (tab.3)
0.6X6.62/10=
0.4 m
0.6X21.8/10=
1.31 ft
H2 (tab.4)
30°C
0.40 m
86°F
1.31 ft
H3 (tab.5)
500 m
0.55 m
1640 ft
1.80 ft
NPHSr
RPM 1000
6.50 m
RPM 1000
21.30 ft
Hz
>(6.5+0.5)+0.4+0.4-(10.33-0.55)=
-1.98 m
Hz
>(21.3+1.65)+1.31+1.31-(33.9-1.8)=
-6.53 ft
Size of pipes and unions G1” 1/2
Summary of Contents for 74.1030.97.3
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