Page 525 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Be st Practice 8 .11 Pump Mechanical Seal Flush Best Practices
chamber pressures and temperatures to change and lead to seal chamber temperature. Flush plans with coolers (21, 23, 41
premature seal wear and/or failure. Note that the stated EROE etc.) have an option for a thermometer downstream of the
low flow range can be reduced if the pump or fluid have any of cooler which can be used to determine the seal chamber tem-
the characteristics noted in Figure 8.11.7. perature. This value must be compared to the PT (pumping
temperature) value listed on the data sheet. If the measured
value does not agree with the data sheet, consult with operations
first to see if process changes can be made. If they cannot be
Pumps with suction specific speeds > 8,000 (customary units) made, discuss the measured temperature with the seal vendor
Double suction pumps
representative. Alternative options for measuring seal fluid
Water pumps with low NPSH margin
Fluids with S.G.< 0.7 temperature are noted in Figure 8.11.10.

Fig 8.11.7 Factors that can reduce low flow EROE range
Temperature gun close to seal gland – be sure to monitor off of
Therefore, we always recommend that the first step in seal a non-reflective surface °
condition monitoring is determination of pump operation within Surface contact thermometer on flush line – add 5 C to
measured value if pipe and use recorded value if SS tubing
its EROE. If the ‘bad actor’ pump is operating outside its EROE,
Install a thermometer in the flush line
we recommend the action shown in Figure 8.11.8. Use an infrared camera to record temperature and temperature
profile

Fig 8.11.10 Alternative methods to measure seal fluid temperature
Consult operations to determine if process changes can be
made to operate in EROE
De fi ne target EROE parameters for operations (flow, amps,
control valve position, delta T) Pressure monitoring

Unless the plant assigned machinery specialist is ‘world class’
Fig 8.11.8 If a centrifugal pump is outside its EROE:
there are usually no pressure gauges in the flush line or seal
chamber. Our recommendations concerning seal chamber
If seal reliability does not improve when operating within the pressure monitoring are presented in Figure 8.11.11. The
EROE, further investigation is required concerning the process measured seal chamber pressure must be compared to the seal
conditions in the seal chamber and/or flush system as noted in vendor’s assumed value, which should be on the seal layout
the remaining sections. drawing. If this value is not present, the seal vendor should be
consulted. Note that the seal vendor assumed seal chamber
pressure is the value that was used in the calculation of the seal
Confirm process conditions are as stated in PV. If the measured value does not agree with the data sheet,
data sheets consult with operations first to see if process changes can be
made. If process changes cannot be made, discuss this fact with
If the ‘bad actor’ pump seal reliability, when operating in the the seal vendor representative.
EROE, does not significantly improve, a complete check of seal
fluid conditions in the seal chamber is required. Figure 8.11.9
shows the process variables that influence seal reliability.
Install a pressure gauge in the seal chamber
Modify the seal flush line for installation of a pressure gauge

1. Seal Chamber Temperature Fig 8.11.11 Seal chamber pressure monitoring guidelines for ‘bad
2. Seal Chamber Pressure actor’ seals
3. Seal Fluid Characteristics:
Cleanliness
Vapor Pressure
Viscosity Seal fluid characteristics
Specific Heat
Specific Gravity If all of the above mentioned items are in accordance with the
seal design (EROE, seal chamber temperature and seal chamber
pressure), a check of the seal fluid characteristics is required.
Fig 8.11.9 Seal reliability and pump fluid conditions are based on:
Figure 8.11.12 presents guidelines for checking the seal fluid
characteristics.
Temperature monitoring If the measured fluid sample parameters are not as stated on
the data sheet, consult with operations first to see if process
Since seal chamber or seal flush line pressure gauges are not changes can be made. If process changes cannot be made, dis-
usually installed on new pumps, the first place to start is with cuss this fact with the seal vendor representative.

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