A mechanical seal is a critical component that prevents fluid leakage where a rotating shaft passes through a pump housing. Installing a cartridge seal properly ensures reliable pump operation and prevents costly downtime. This guide walks you through the complete installation process, from preparation to final testing, providing clear instructions for maintenance technicians and engineers.
Preparation and Safety Precautions
- Lock-Out/Tag-Out: Before any work, fully isolate and de-energize the pump. Lock out the power supply and ensure the driver (motor or engine) cannot start. Close valves and relieve pressure in the pump casing.
- Drain and Depressurize: Drain the pump and flush it if it handled hazardous or hot fluids. Allow the equipment to cool to a safe temperature.
- Clean Work Area: Work in a clean environment. Lay out clean tools and prepare a clean surface to place disassembled parts.
- Verify Replacement Seal: Confirm you have the correct cartridge seal for the pump model and service. Check the new seal’s specifications against the pump vendor manual and maintenance records to ensure it’s the proper type and size.
Tools and Materials Needed
- Wrenches and Socket Set: For removing the old seal’s gland bolts and installing the new seal’s gland.
- Allen (Hex) Wrenches: Most cartridge seals use hex drive set screws (drive collar screws) to clamp the seal to the shaft.
- Torque Wrench: To tighten gland bolts (and possibly set screws) to the specified torque.
- Dial Indicator (Optional): Useful for checking shaft runout or alignment of the seal chamber face. This can verify the gland will sit square (total indicated runout within ~0.005″).
- Cleaning Supplies: Solvent (compatible with the pump fluid), lint-free rags, a soft brush, and fine emery cloth or a file.
- Lubricants: A thin film of silicone grease or manufacturer-supplied lubricant for O-rings and the shaft/sleeve will help installation. Use a lubricant compatible with the seal materials and pumped fluid (often a water-based or silicone lubricant is recommended; avoid petroleum grease on EPDM, for example).
- Miscellaneous: Screwdrivers or pliers (for removing old packing or seal components), a rubber mallet (to gently loosen components if stuck, never to force the new seal). Having the pump’s instruction manual on hand is also advisable.
Pump Disassembly and Old Seal Removal
- Depressurize and Disassemble: Ensure the pump is drained and isolated. Disassemble the pump as needed to access the seal. In many centrifugal pumps, this means removing the coupling guard and disconnecting the coupling, then unbolting the pump’s seal gland or stuffing box cover. If it’s a back pull-out design, you may remove the entire rotating assembly.
- Handle Old Seal with Care: Be cautious of sharp edges or broken components – old seals can have cracked faces or sharp shims. Note how the old seal was oriented. Remove all pieces of the old seal, including any stationary seal ring still in the housing and any drive pins or collars on the shaft.
- Inspect Shaft and Casing: Examine the shaft or shaft sleeve where the seal sits for any scoring, wear rings, or burrs.
- Remove Burrs and Clean: Gently file down any burrs on the shaft and keyway that could damage the new seal’s O-ring during installation. Use fine emery cloth to smooth the shaft surface. Wipe all surfaces with a compatible solvent and lint-free cloth until clean and dry.
- Prepare Flush Connections: If the seal chamber has flush or quench ports (auxiliary piping), disconnect or plug these lines before cleaning to prevent debris entry. Flush out any sediment in these passages. Clean and flush all piping connected to the seal (flush plans, quench lines) so no contaminants will be introduced to the new seal.
Installing the New Cartridge Seal Assembly
- Position the Seal Assembly: Gently slide the cartridge seal assembly onto the shaft, taking care not to strike the seal faces. If the seal has a split ring or drive collar, keep it loosely assembled as you move it into place. Slide the seal until the gland plate meets the seal chamber (stuffing box) face. The cartridge sleeve and its O-ring will slip over the shaft – go slowly to avoid O-ring damage. If there is a keyway or sharp step on the shaft, consider wrapping it with tape temporarily to protect the O-ring during this step, then remove the tape.
- Align and Seat the Gland: Rotate the cartridge seal gently so that the gland bolt holes line up with the threaded holes on the pump’s seal chamber. Also orient any flush/vent ports on the gland to the desired positions (e.g. usually the vent or flush outlet should be at top dead center) according to the seal plan. Start the gland bolts by hand, tightening evenly crosswise finger-tight. As you do, ensure the gland plate sits flush against the seal chamber face without any gap. If the gland has anti-rotation pins or fits into a register on the pump, make sure those engage correctly.
- Tighten Gland Bolts Evenly: Using a torque wrench, tighten the gland nuts/bolts in an alternating, star pattern. Draw the bolts down in small increments to the specified torque (refer to the seal or pump manual for torque values). For a quality installation, if available, mount a dial indicator on the shaft and sweep the seal chamber face by rotating the shaft – the total indicated runout (TIR) should be within about 0.005″, confirming good alignment.
- Set the Drive Collar (Set Screws): Most cartridge seals have a drive collar (or set of set screws) that locks the rotating part of the seal to the shaft. Ensure that the set screws are positioned over a clean, unmarred section of the shaft (if the old set screws left a groove or mark, stagger the new screws away from that line if possible). Tighten the set screws evenly and firmly: for example, if there are multiple screws, turn each a few quarter-turns in succession rather than one screw fully at once, so the collar clamps uniformly.
- Remove Setting Clips/Plates: The cartridge seal is shipped with setting clips or spacer pins that kept the seal faces apart and correctly positioned during installation. Now that the seal is clamped and secured, remove all setting clips or pins per the seal instructions. Typically, this involves unscrewing or unclamping the clips from the gland and sliding them out. Make sure no clip is left engaged with the sleeve or drive collar.
- Rotate Shaft to Check: After the clips are removed, manually rotate the pump shaft (or rotor) at least one full turn to ensure that everything moves freely. You should feel smooth rotation.
Reassembly and Final Adjustments
- Pump Reassembly: Reinstall any pump parts that were removed for access. This may include the impeller, shaft sleeve, bearing housings, or pump cover depending on the design.
- Coupling and Alignment: Reattach the pump coupling to the driver (motor) if it was disconnected. Align the coupling carefully according to manufacturer specifications (check for proper gap and angular alignment with feeler gauges or dial indicator).
- Reconnect Flush Lines: If the seal uses an external flush, quench, or buffer fluid, reopen the valves or reconnect the piping that was isolated. Ensure that cooling or flush support systems are functioning (e.g. cooling water flowing, barrier fluid pressurized to the correct level for dual seals, etc.). Any vent ports should be bled of air so the seal chamber is completely full of liquid and not vapor-locked.
Post-Installation Checks and Testing
- Static Pressure Test: If possible, perform a static leak test prior to running the pump. This can be done by pressurizing the seal chamber or the pump casing (with fluid) to a certain test pressure.
- Initial Startup: Ensure the pump and seal chamber are fully vented of air and filled with fluid (the seal faces must have liquid lubrication). Never start the pump dry. Start the pump under controlled conditions. It’s wise to run at low speed or briefly bump start the pump and then stop, to observe the seal. Check that the seal is running smoothly (no abnormal noise or vibration from the seal area).
- Monitor for Leaks: With the pump running, closely watch the seal gland for leakage. A new mechanical seal should run with essentially zero visible leakage—at most, a slight vapor or occasional drop might be seen, depending on design. Also monitor the seal flush pressure/flow (if applicable) and ensure it’s within required range.
- Observe Temperature and Vibration: During the test run, feel the area around the seal gland (if accessible and safe) – it should not be rapidly heating. A slight warm-up may occur, but overheating indicates a problem (like dry running or excessive friction). Listen and feel for vibration; if the pump or seal exhibits significant vibration, shut down and investigate (could indicate misalignment or other issue).
