Magnetic Drive Pumps
(1) Taking the shaft power at SG=1 from the performance drawing, e.g. #kW
(2) Required shaft power(kW) = #kW x SG of the liquid x safety factor
* Suggested "safety factor":
MX / MDH 5~10%
MXM / MDF-L 10~15%
MDM / MDE 15~20%
* As viscosity of liquid increases, the required shaft power, flow and head will be affected.
Performance compensation must be calculated.
(1) In general, cavitation will be generated if the pressure in the pump body is lower than the saturated vapour pressure of liquid.
(2) With increasing of flow rate, the value of NPSHa decreases while that of NPSHr increases.
(3) In order to avoid cavitation, make sure that NPSHa ≧ NPSHr + safety factor (about 0.5m).
NPSHa = [10E6(Pa – Pv) / pg ] ± hs – hfs
** Pa : Absolute pressure on liquid surface at suction side (0.1013 MPa for atmospheric pressure)
Pv : Vapor pressure of liquid temperature at suction side (MPa)
p : Density of liquid (kg/m3)
g : Gravitational acceleration (9.80665 m/sec2)
hs : Height from the lowest liquid surface at suction side (m)
+ for flooded suction
- for lift suction
hfs : Pipe resistance at suction side (m)
The following measures may be adopted:
(1) Installation of pump at a lower level.
(2) Reduce the resistance of suction piping.
e.g. Increase the piping diameter
Eliminate the accessories of the suction piping
(3) Lower the working temperature of liquid so as to lower its vaporized pressure.
(4) Without scarify the required flow and head, reduce the pump speed.
Basically, "MD" series magnetic driven pump is designed for indoor operation, but not outdoor installation.
It is because the “spindle” and “thrust ring” of “MD-F / MX-F” series magnetic driven pump are made of “SiC”. Although “SiC” is hard in nature, it is also fragile with tough strike.
Make sure to follow the instruction on “How to start magnetic driven pump” as follows.
(1) Make sure that the pump chamber is filled with liquid but no more air inside.
(2) Open the suction valve completely, but close the discharge valve.
(3) Start the motor momentarily (within a second), repeat this action 2 to 3 times, then start the motor in normal.
(4) Open the discharge valve gradually until the working point is reached.
Yes, it is essential to keep a minimum flow. Magnetic driven pump is not allowed to operate continuously without discharge. Please refer to the operation manual or performance drawing for the requested minimum flow.
"MDM" series magnetic driven pump may handle liquid between -20 ~ 105℃ with limited condition. Please consult with Iwaki.
粤公网安备 44010502002553号