Burks 21727 Mechanical Seal 0.500 in Shaft for CR series
This is the mechanical seal Burks lists as part 21727, sized for a 0.500 in shaft, with Carbon, ceramic and Buna-N components, on CR series pumps. The sealing happens across a lapped face pair so flat that the film of liquid between them is thinner than a human hair.
Nothing kills a mechanical seal faster than running dry. Without liquid between the faces the film is gone in seconds, friction spikes, and the carbon face heat-checks or the seat cracks. After that the seal drips and will keep dripping. Abrasives do the same job more slowly, scoring the faces until they no longer mate, and a hardened elastomer boot lets the rotating face stop tracking the shaft.
Shaft size and elastomer both have to match. This seal is built for a 0.500 in shaft, and the Carbon, ceramic and Buna-N specification sets the temperature range and the liquids it will tolerate. Burks lists the same shaft size in several compounds, so confirm both before ordering; this one is listed for CR series pumps.
Key Features
- Genuine Burks mechanical shaft seal assembly
- 0.500 in shaft - matches the original shaft dimension
- Carbon, ceramic and Buna-N construction
- Listed for CR series pumps
- Spring loaded and self-adjusting as the faces wear
- Supplied complete - rotating face, seat and elastomers
Applications
- Burks CR series pump rebuilds
- Curing a persistent drip from behind the pump casing
- Recovery after a dry run or a lost prime
- Replacing seal faces scored by grit or abrasives
- Planned maintenance on duty and standby pumps
- Industrial, marine and dockside pump installations
Specifications
- Brand: Burks
- Manufacturer: Crane Pumps and Systems
- Manufacturer Part Number: 21727
- Part Type: Mechanical shaft seal
- Material: Carbon, ceramic and Buna-N
- Size: 0.500 in shaft
- Fits: Burks CR series regenerative turbine pumps
- Condition: New
Frequently Asked Questions
Q: Can I touch the lapped faces while fitting it?
Keep your fingers off them. The faces are polished to within a fraction of a light band and skin oil or a single hard particle left on them will hold them apart. Wipe with a clean lint-free cloth, use the recommended lubricant, and press home with even pressure.
Q: Should anything else be changed at the same time?
Check the shaft or sleeve where the elastomer grips it. A groove worn at the old seal position will chew the new boot in short order. The casing joint seal is also worth renewing, since it has to come off to reach the seal anyway.
Q: How long should a mechanical seal last?
Years on clean liquid with a flooded suction. Life falls sharply with abrasives, with frequent starts on a starved inlet, and with temperatures near the top of the elastomer rating. Most premature failures trace back to operating conditions rather than the seal itself.
Q: A few drops appear when the pump first starts. Is that normal?
A very light initial weep while the faces bed in can settle within an hour or so of running. A steady drip, or anything that continues beyond that, means the faces are not seating and the seal needs to come back out.
Not sure this is the right part? Send us a Picture of the pump plate on your pump and the CLR Marine team will confirm the correct mechanical seal before you order.
CLRMarine
