Always execute the following seal installation best practice guidelines for component and cartridge mechanical seals to achieve maximum pump mechanical seal MTBFs:
- Component seal faces must be cleaned with clean cloth and rubbing alcohol (or alcohol wipe) just before installation. Proper care must be taken to not touch the faces after cleaning.
- Limited grease should be used on seal gland ‘O’ ring as it can migrate to the seal faces and cause damage. Proper practice is to sparingly apply grease to ‘O’ ring then install it in the gland. This will ensure ‘O’ ring will stay in the groove when installing the seal.
- Use liquid soap sparingly on sleeve ‘O’ ring to assist in installation.
It is recommended that this best practice be incorporated into the plant maintenance procedure manual for mechanical seal installation.
Component mechanical seal installation
- Refer to the vendor instruction book and obtain all required mechanical seal components.
- Have a clean area available for the components and ensure that there are no finger prints, oil or grease on the primary seal faces. Wipe with alcohol using a lint free cloth if necessary.
Primary seal face flatness will have been confirmed by the seal manufacturer and should be within 1-2 helium light bands. For this reason, the primary seal faces must be free of fingerprints, oil and/or grease.
Inspect the rotating head assembly as follows:
Secondary ‘O’ ring in pusher seal – inspect for discontinuities, confirm proper material and durometer. (Note: Do not lubricate ‘O’ ring.)
- Ensure that all springs (if a pusher seal) are sitting upright and have not been dislodged from their counter-bores.
- Confirm that shaft or shaft sleeve surface finish, where secondary ‘O’ ring or Teflon wedge will ride, is maximum of 32 rms, using a comparator.
- Clean and de-burr the shaft area and seal chamber area as required using a solvent that will be compatible with the process fluid. (Note: Assure all piping/tubing is isolated from flush/quench ports. Plastic plugs need to be installed in all flush/quench after isolation of piping/tubing, up to the point of the piping/tubing reinstallation.
- Install the seal head carefully being sure not to damage the secondary ‘O’ ring, or the ID of the primary ring on the shaft/sleeve.
- Proper spring compression check (‘working height’) – obtain dimension from seal drawing which shows the distance between the back of the seal retainer and the seal chamber face. Then fit the bearing bracket and shaft up against the casing and mark (with bluing pen) the point on shaft or sleeve directly below the seal chamber face. Remove shaft bearing bracket from casing and mark the dimension where the back of the retainer sits when assembled.
- Attach seal head to shaft/sleeve and ensure that set screws are installed on clean and undamaged shaft areas. If this is not possible, carefully de-burr with a file and smooth out with emery cloth.
- Note: If sleeve ‘O’ ring is installed, confirm proper material, size and durometer and apply a small amount of ‘Krytox’ or equal lubrication and install. Assure shaft surface is clean and free of any burrs and carefully install sleeve being sure ‘O’ ring is not damaged.
- Install the stationary seal face into gland evenly to ensure face is not cocked. Assure that any finger prints are removed with alcohol and lint free towel.
- Stationary ‘O’ ring checks – confirm proper material, durometer, and inspect for discontinuities.
- Install gland to stuffing box using opposite and even tightening technique. Prior to doing so, a sweep of the seal chamber face is required to ensure proper sealing between gasket/’O’ ring on seal gland and seal chamber. A dial indicator should be attached to the shaft and the shaft will be rotated to cover a complete sweep of the seal chamber face. TIR should be no more than 0.005’.
- After seal is completely installed, conduct a static pressure check. Consult the seal vendor for the proper pressure if static limit is not indicated on seal drawing. If any leaks are observed, consult seal vendor immediately.
Typical installation errors:
Contaminated faces – can affect face flatness, resulting in excessive leakage. In addition, certain oils can set-up like adhesives and pull material out of the carbon primary ring faces after start-up, resulting in pre-mature seal failures.
Applying lubricant to secondary seals which can enter primary seal face areas – the same results apply as above.
Not setting proper spring compression: excessive compression – more seal wear. Low compression – will not provide sufficient face contact during start-up and standby conditions allowing excessive leakage.
Improper installation of mating ring into the gland resulting in excessive leakage due to improper face contact. Note that if back of mating ring is visibly ‘not flat’, the same result can apply. Stuffing box face TIR should be checked with dial indicator on shaft. Seal chamber face flatness should be no more than 0.005’ TIR.
Installation of gland to stuffing box not using equal and opposite tightening technique. Failure to tighten the nuts/capscrews properly can cock the mating ring, which will not allow for proper contact between the faces and result in excessive leakage between the seal faces.
Sleeve ‘O’ ring cut during installation, resulting in excessive leakage between shaft and sleeve.
Cartridge mechanical seal installation
- Refer to pump vendor manual and maintenance records to ensure proper cartridge seal will be used.
- Assure that the seal chamber is cleaned and shaft is de-burred to remove any sharp material that could damage seal sleeve ‘O’ ring.
- Assure seal chamber is isolated from all flush and quench connections systems. Plastic plugs need to be installed in all flush/quench after isolation of piping/tubing up to the point of the piping/tubing installation.
- Assure that the proper durometer, material and size ‘O’ ring with ‘Krytox’ or equivalent lubricant.
- Slide sleeve over shaft carefully.
- Install gland to seal chamber using equal and opposite tightening technique. Prior to doing so, a sweep of the seal chamber face is required to ensure proper sealing between gasket/’O’ ring on seal gland and seal chamber. A dial indicator should be attached to the shaft and the shaft will be rotated to cover a complete sweep of the seal chamber face. TIR should be no more than 0.005’.
- Tighten set screws to engage shaft/sleeve by equal and opposite technique. Assure that a clean shaft surface is available for all set screw locations. If not, use a file and emery cloth to remove any damaged spots. Be sure to completely clean shaft to remove all debris.
- Completely remove setting clips. If setting clips are slid up on the gland, they can potentially fall back down to the sleeve or drive collar resulting in an ignition source (the writer has experienced fires that have started due to this issue).
Failure to have and implement a required mechanical seal installation procedure has been a principal cause of low mechanical seal MTBFs (lower than 12 months).
FAI has used this best practice since the 1990s to ensure that plant mechanical seal installation procedures are in complete accordance with mechanical seal vendors’ recommendations and to ensure optimum installed seal safety and reliability.
