By PumpWorks Engineering Team / August 8, 2022
The rotating shaft of a centrifugal pump penetrates the back end of a pump casing through a stuffing box or seal chamber. The primary purpose of a mechanical seal in a centrifugal pump is to prevent fluid from leaking to the atmosphere along this rotating shaft. Selection of the right mechanical seal for each pump application is critical when considering safety and reliability. Mechanical seal failure is typically one of the primary reasons why pumps fail. In this guide, the experts at PumpWorks will show you the steps to install a mechanical seal in your centrifugal pump with minimal downtime.
A mechanical seal requires two extremely smooth and flat (lapped) seal faces in contact, one rotating with the shaft and the other stationary with the casing. These seal faces are sealed to their appropriate holders through the use of secondary seals (o-rings or gaskets). The faces are mechanically energized and flexible so that they can be placed into contact and move to make up for static and dynamic misalignments as well as wear. The seal faces require lubrication from the fluid and break down this fluid as it tries to escape through the seal faces, resulting in slight vapor release. All mechanical seals leak…vapor…when selected and sized correctly.
You may be wondering how long the mechanical seal installation procedure will take. By following the 10 simple steps listed below, you’ll have the job done in no time.
The first step is to power off the centrifugal motor so that it is not in motion. Shut down the main power supply and double-check that there is no chance of the machine starting up again. Once this is done, it’s time to get to work!
Shut both inlet and outlet isolation valves and then drain the pump casing by removing the casing drain plug.
If your pump is a ‘back pull-out’ design, remove the spacer element in the pump coupling. Then remove the casing bolts and slide the remainder of the pump away from the casing. You are now able to access the mechanical seal without having to disconnect the casing from the inlet and outlet piping. If the pump is not a ‘back pull-out’ design, you will need to disconnect the complete pump after disconnecting the coupling between the pump and motor shaft. If the pump is a close coupled design (the pump uses the shaft of the motor as its shaft and the motor directly bolts onto the back of the pump), you will need to remove the entire pump/motor. Remove the casing bolts and remove the casing.
The mechanical seal is located behind the impeller on the pump shaft. Impellers are either screwed onto the shaft or held in place via a bolt. To remove the screwed-on impeller from the shaft, use a wrench to hold the shaft in place and rotate the impeller clockwise until it is completely unscrewed. To remove a bolted impeller, hold the shaft in place and remove the bolt.
You can now directly access both the rotary and stationary seal parts. The rotary parts are typically held in place along the shaft using set screws. Remove the set screw and slide off the rotary seal parts. Remove the stationary part of the seal from the casing or seal chamber bore.
Now it’s time to place a new mechanical seal onto the shaft. Carefully slide the replacement seal parts along the shaft. Using a new o-ring or gasket material, press the stationary part into the casing or seal chamber bore. Follow the instructions for setting the rotary portion back onto the shaft correctly. This is a crucial step.
CAUTION: Always install mechanical seals in a clean working space. Don’t touch the front of the seal faces as it is susceptible to body oils and may not function properly if compromised. Keep the seal in its packaging until it’s time to install.
Use your wrench to hold the shaft in place while you screw the impeller onto the pump’s shaft using a new impeller o-ring or gasket. Or use the impeller bolt and a new o-ring or gasket to attach the impeller to the end of the shaft.
For back pull-out designs, slide the back pull-out assembly up against the installed casing and bolt it in place. Checking pump alignment will be necessary after step 9 below. For close coupled or non-back pull-out designs, reinstall the casing using the casing bolts. In all cases, torque the casing bolts in accordance with the pump Installation, Operation, and Maintenance (IOM) manual.
For back pull-out designs, the only steps remaining are to reinstall the spacer element to the existing coupling hubs along the pump and motor shaft, and make sure the mounting feet of the back pull-out assembly are bolted back into place on the pump baseplate. Realign the pump and motor. For close-coupled pumps, place the pump back and reconnect the inlet and outlet piping. For non-back pull-out pump and motor designs, replace the pump on the baseplate, reconnect the inlet and outlet piping, re-bolt the pump to the baseplate, reconnect the coupling and then realign the pump and motor.
Make sure you have refilled the pump casing by opening the inlet and outlet isolation valves. Some pump designs will require venting, so refer to your pump IOM. Before starting the pump, it is always a good idea to re-verify the rotation of the motor to make sure it is correct. This is done before reconnecting the pump and motor coupling. Bump the motor and verify rotation. Then reconnect the coupling, and the pump is ready to start.
Always review safety precautions found in the pump IOM. Always use the Pump IOM when working on any pump. Install the mechanical seals using the specific instructions from the mechanical seal manufacturer. Lastly, always make sure the pump and motor are realigned within 001” – 002”. Misalignment will cause premature mechanical seal failure.
PumpWorks is the go-to company for all your mechanical seal installation needs. Our pump manufacturing company offers over 30 years of experience in the troubleshooting, selection, application, and repair of mechanical seals. We serve a wide range of process industries such as petroleum refining, chemical, food and beverage, water and wastewater, power, and more.
Our highly trained seal specialists and in-house industrial pump repair teams can service and repair all types of seals.
Check out our blog for more helpful tips and resources.
Call PumpWorks today at 855.979.9139 or contact us online to learn more.
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1
Separate the pump housing - Most pumps have either a large metal clamp ring or a series of nuts and bolts the hold the pump housing to the motor plate. Using a socket or crescent wrench, remove the nut that is securing clamp together or loosen and remove the series of nuts and bolts. Some banded pumps have a hand knob instead of a nut holding the clamp together. Slide back the half of the pump assembly with the motor attached. Try to place the pump on a suitable work surface. Note: You can either leave the electrical conduit intact while doing this procedure or if you require more space you can disconnect the wires form the motor. Be sure the POWER IS OFF and note the wiring so you reattach the wires the same way![1]Using a socket or crescent wrench, remove the nut that is securing clamp together or loosen and remove the series of nuts and bolts. Some banded pumps have a hand knob instead of a nut holding the clamp together. Slide back the half of the pump assembly with the motor attached. Try to place the pump on a suitable work surface. Note: You can either leave the electrical conduit intact while doing this procedure or if you require more space you can disconnect the wires form the motor. Be sure the POWER IS OFF and note the wiring so you reattach the wires the same way!
2
Expose the Impeller - Remove the screws from the impeller cover (diffuser).Remove the impeller cover (diffuser). Be sure not to lose any of the screws!
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3
At this stage it is very important to inspect the impeller for damage since you have the pool pump open. The impeller is one of the more likely pump components to develop wear or damage and inspection at this stage can save you the headache of needing to open and repair the pump a second time in the future.[2]The impeller is one of the more likely pump components to develop wear or damage and inspection at this stage can save you the headache of needing to open and repair the pump a second time in the future.
4
An impeller can show signs of heat damage and be melted or the leading edge of the impeller fins could be pock marked if the impeller has been exposed to cavitation. Replace the impeller if it shows any signs of damage.[3]Replace the impeller if it shows any signs of damage.
5
Remove the Impeller - You will need to stop the motor shaft from turning while you rotate the impeller counter-clockwise to remove it. The use of vice grips to hold the shaft is never recommended. Instead, remove the cap from the center of the motor on the end opposite the shaft, and use a screwdriver or open-end wrench to prevent the shaft from turning. Unscrew and remove the impeller.[4]The use of vice grips to hold the shaft is never recommended. Instead, remove the cap from the center of the motor on the end opposite the shaft, and use a screwdriver or open-end wrench to prevent the shaft from turning. Unscrew and remove the impeller.
6
Remove the seal plate - Remove the (seal plate) from the motor to gain access to the motor shaft. Usually there will be 4 bolts that hold the seal plate to the motor. You will need to remove the impeller before you can remove the seal plate.[5]Usually there will be 4 bolts that hold the seal plate to the motor. You will need to remove the impeller before you can remove the seal plate.
7
Remove the old seal assembly - Using a pair of channel-locks, pull off the old pump spring seal from the motor shaft. Inside the center of the seal plate is the ceramic part of the pump seal. Be careful not to damage the plastic of the seal plate. You can also push it out from behind instead, using a screwdriver knock out the old ceramic seal. Note: Be sure the rubber ring seat is removed with the ceramic portion also.
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8
Clean and prepare to replace the seal - Lightly wipe off the motor shaft and the seal plate. Inspect the seal plate for damage, cracks, melted or out of round will cause the pump to leak even with a new seal. Carefully inspect the impeller for cracks or breaks.
9
Install the new seal assembly - Note: NEVER touch the FACE of the ceramic with anything metallic or greasy, because you could destroy the integrity of the pump seal. Press the ceramic part of the seal into the seal plate... using clean fingers to get it seated. (The rubber part towards the seal plate, the white ceramic facing away from the motor.)Slide the spring seal part over the motor shaft. Push it past the threads.( Black carbon face of the spring side needs to make contact with the white ceramic side).Do NOT LUBRICATE this seal with anything besides water! If you do, then it could end up slipping against the impeller, and eventually overheat, destroying the seal.
10
Replace the Impeller - Using the Vice grip method mentioned previously, hold the motor shaft to prevent rotation, and then screw on the impeller. HAND TIGHT. The rotation of the pump motor will keep it tight.
11
Replace the Diffuser - Now realign the diffuser, and tighten the screws. Ensure that the impeller does not touch or interfere with the diffuser, by rotating it with you finger.
12
Re assemble the pump and motor - Inspect and lube the large seal plate o-ring for cracks or damage. If it's flattened or stretched out, it may need to be replaced. Be sure the clamp is 'around' the outside rim on both sides of the seal plate and the pump housing. This can be a little tricky to get aligned. Tighten the retaining band with a wrench or socket, or if your pump has a knob, use your hand to tighten it. If you pump uses nuts and blots reassemble and tighten.
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