The mechanical seal is critical to the overall performance and durability of a centrifugal pump. It is designed to prevent fluid from leaking from the rotating shaft. Mechanicals seals feature two smooth and flat seal faces. One rotates with the shaft, while the other remains stationary with the pump casing. The seal faces are flexible and will move in conjunction with rotation to make up for any slight misalignments and wear.
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There are many different types of mechanical seals, including single-cartridge and multi-cartridge designs. A poorly sized, installed, or maintained seal can lead to serious pump problems. In fact, mechanical seal failure is one of the most common issues in centrifugal pumps. Selecting the right type of seal for your pump is crucial'so is installing it correctly. Below are eight steps you should take when installing a new mechanical seal on your centrifugal pump:
The first step is fairly obvious. Cut power to the pump motor, and turn off the main power supply. There should be no risk of the equipment starting up during mechanical seal installation or maintenance!
Close inlet and outlet isolation valves. Remove the pump casing drain plug, and drain the casing of fluid.
Depending on the configuration of your centrifugal pump, this step may be slightly different. You may have a back pullout design or not. Follow the necessary steps to disconnect the pump casing, or pull out the casing to access the impeller and mechanical seal for removal, maintenance, or installation.
The mechanical seal sits behind the impeller on the pump shaft. There may be screws or a bolt to remove to disconnect the impeller and access the mechanical seal.
Whether you are upgrading the factory seal or replacing a worn mechanical seal, you need to remove the existing seal from the shaft and casing. In most cases, set screws are used to hold the seal components in place. Unscrew those to remove both the rotary seal parts and the stationary part of the mechanical seal.
Assuming your new mechanical seal is properly sized and configured to match your pump, you can now install it. This should always be done in a clean workspace, and you should avoid bodily contact with seal faces throughout the process. Natural oils can compromise the lubrication and seal faces. Follow the proper instructions to install each component of the new seal, along with a new O-ring or gasket.
From here, you simply work backward through the same process. Once the mechanical seal is installed, you are ready to reinstall the impeller and reconnect the pump casing. The pump should be put back together properly with all the same pieces in the correct places. Don't forget to open the inlet and outlet valves to refill the pump casing. Some centrifugal pumps may require additional venting during this step. The pump and motor should be realigned with a tolerance of .001''.002' to avoid mechanical seal failure.
Once the new mechanical seal is installed and the pump is reassembled, you can reconnect the power supply and turn on the pump. Let it run for a while to ensure everything works correctly. Check the shaft for any fluid leaks, and perform all necessary safety procedures.
If you follow these simple steps, you can install a new mechanical seal easily. The biggest challenge for most operators is selecting the best mechanical seal for the equipment and application. Many different options are available, and installing the wrong seal (or installing it incorrectly) could have disastrous consequences.
DXP Pacific is here to help with your mechanical seal selection, installation, and maintenance needs. We work with some of the world's best mechanical seal manufacturers like John Crane, Flexaseal, Flowserve, Chesterton, and AES. Contact us today and find the best mechanical seal solutions for your centrifugal pump.
By PumpWorks Engineering Team / August 8,
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.
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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.
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