This procedure should be viewed as guidance to give the owner advice in verifying that the motor is operating in the correct rotation. It is not a guarantee of the correct rotation, as, at all times, good judgment must be utilized.
It is very important that:
- Correct rotation is checked during the three (3ea.) bump checks detailed in the manual.
- The aforementioned bump checks are not only performed to remove (burp out) any remaining air that may have been trapped during the fill and purge procedure, but they also provide the means to verify correct rotation prior to continued operation.
- Incorrect rotation (reverse rotation), if allowed to operate over several hours, can and most likely will cause premature motor problems and/or failure.
After installation and after the fill and purge procedure has been completed; the following checks should be performed prior to the first 5 second bump:
- Low-pressure cooling water flow is established at the correct flow and temperature through the low-pressure side of the heat exchanger.
- The correct voltage is supplied to the motor as per the OEM manual.
- All valves are in the correct position according to the customer boiler operating procedures.
- All safety permits (Permits For Work, etc.) are cleared (mechanical and electrical) as per the local site procedures.
- All needed personnel are in position.
- Communication between the control room and the operators at the equipment is checked and established. (note: It is always a good idea to position an operator at the main breaker, as there have been times when the motor has failed to shut down from the control room trip).
- Once all precautions are realized and addressed to customer satisfaction, the 5-second bumps can commence.
There are several different ways to help in verifying the correct rotation. This procedure will take each one and address it in some detail. Below are 7 typical things to monitor, to aid in the verification process:
- Differential pressure
- Drum level
- Motor Amps
- Discharge check valve(s)
- Phase rotation equipment
1. Differential pressure
- Differential pressure is the easiest way to verify correct rotation. Check if the following is present and working correctly:
- There is a differential pressure gauge at the pump and/or in the control room and they are working correctly.
- If the BWCP is operating in the correct rotation the differential pressure will match the values in the manual or normal site historical operational data. As a rule of thumb, operating in the reverse direction will cause about 70% of the expected differential head.
2. Drum level
- This method can only be used on a drum-type boiler (controlled circulation). With natural circulation (supercritical) boilers, a steam drum is not used.
- Most control rooms have a steam drum level indicator. Upon start-up of a motor, if it is operating in the correct rotation, there should be a drop in the drum level corresponding to the surge in circulation being flow with the BWCP starting. It is essential that instrumentation is working properly to use this method.
- This will need to be monitored from the control room.
3. Motor Amps
- Motor amps can be used however is sometimes the hardest method to rely on. This is due to several reasons:
- The length of time (5 seconds) does not give much time for the amps to be recorded.
- Most times the boiler water is “cold” which will give a higher amp reading due to the S.G. of the water.
- Note: It is a good practice to have an electrician at the switchgear with an amp meter. Most times, the electrician is able to get a reading, before the motor is shut down.
Note: On most BWCP’s motor amps are “HIGHER” than normal if the motor is in the “WRONG” rotation; however, on some motors the amps for forward and reverse rotation may be very close.
4. Check valves
- More times than not, a very good indication to verify the correct rotation, is to listen for the opening and or closing of the discharge check valve upon starting and shutdown of the motor.
- This method is successful a high percentage of the time in the verification of rotation. However, as with all the methods, it is not guaranteed and good judgment must be utilized.
- These large check valves are generally of the “floating plug, non-return type”. The plug is free to float. The stem itself is not attached to the plug but acts as a means to seat the plug by applying a force to the plug with a stem that pushes down onto the plug when closing. As the stem is opened it moves up and leaves the plug free to float with the pressure of the fluid.
- If the BWCP is operating in the correct rotation, the plug (provided it is in working condition, not stuck and or “hanging up” due to lack of maintenance) will be pushed open and when the motor is shutdown it will fall back down on its seat and make a “clunking sound” that most times can be heard.
- If one or more circulators are running during the “bump” check, due to the backpressure from the other pumps, the closing of the check valve is even more pronounced.
- If the closing of the plug is not heard, more times than not, the motor is in the wrong rotation due to the fact that it did not push the plug off its seat.
- Often if the motor is operating in the wrong rotation, there will be a noise in the pump end that sounds similar to cavitation.
- With the correct rotation, the motor will be smooth and noise-free.
- If a flow gauge is utilized, then flow can be checked. However, this is normally not available at the majority of plants in this application.
7. Phase rotation equipment
- If the customer has or has access to a phase rotation meter this can be the best way to verify rotation before the motor is installed.
- The plants know their A-B-C phases coming from the switchgear, therefor a phase rotation meter can be used to verify phase on the motor.
- The best thing about this method is that it is used before the motor is installed and it only requires a very small amount of movement to the motor rotor once the phase rotation meter is attached.
- With this method, there is a good comfort level before the motor is installed that it will operate in the correct rotation and the previous methods (1-6) can be used as a verification check.
Once again, this procedure is only an attempt to aid the customer in verifying the correct rotation of the BWCP. If you have any questions regarding this procedure please conact your local salesman or complete the form below and we will get back to you as soon as possible.