Dear K.Netipong,
As checked with our factory, the required pumping condition (Flow: 4.5 m3/h and head 190 m) is not suitable to use magnetic pump.
It can be seen in pump curve of the existing pump as below.
It is very close to minimum flow (min flow: 4.03 m3/hr) which it cause of vibration and possibly to run dry.
Moreover, it operates just only 11% of Best efficiency point (Recommend 80 to 110% of Best efficiency point)
So, we recommend to change type of pump to be overhung type with double mechanical seal.
Please help check if it is acceptable krub.
If it is acceptable, we will submit you the quotation shortly.