The Essential Guide to Your PSS Shaft Seal

July 21, 2014 - 10:00 AM by Samantha Pudney

When it comes to marine mechanical seals, there is only one seal that is considered standard equipment in many reputable boat builders and yard across the globe, and that the PSS (Packless Sealing System) Shaft Seal. Its manufacturer, PYI Inc., opened its doors in 1981 and is known for rapidly responding to customer input, using their comments and critiques to better their products. PYI Inc.’s main goal is to provide only the best in quality marine equipment with an unbeatable level of customer support and satisfaction.

Boat builders and yards have good reasons to put so much faith in PSS Shaft Steals. They have been certified by Bureau Veritas and ABS & Rina. Builders and yards can easily see the advantages of PSS. Traditional packing type glands often require quite a bit of maintenance and constant adjustments, which leads to extra unforeseen costs. Additionally, PSS are 100 percent water-tight and will eliminate water in the bilge. This will also lessen the wear to the propeller shaft. These shaft seals also come in a range of sizes and can be easily fitted to just about any vessel.

PYI Logo

What is a PSS Shaft Seal?

As a sailing enthusiast or commercial shipper, you’ve probably heard about the PSS Shaft Seal without truly knowing what it is or what it does. Simply put, it’s a mechanical face seal that is made between flat surfaces of the rotating stainless steel rotor and the stationary carbon flange. This flange is attached to the vessel stem tube using hose clamps, and it is also attached to the front side of the bellows using hose clamps as well. The rotor is fitted on the shaft just in front of the carbon flange and is used to compress the bellows before the collar is secured to the shaft with set-screws.

This compression keeps contact between the faces and lets the PSS compensate for most misalignment and vibration problems. The stainless steel collar is sealed to the shaft using two o-rings that have been recessed into the bore of the collar. The o-rings will rotate with the shaft and rotor. They do not experience wear during this operation.

In short, this means that PSS Shaft Steals are mostly maintenance free, though check-ups are required. They’re incredibly strong and durable. They also resist high temperatures, UV radiation, salt water and most importantly corrosion.

PSS Shaft Seals


If you don’t have much experience with engine mechanics, it’s probably best to have a professional do this for you. However, there are many great tutorials available online and even on PYI Inc.’s website. This is an extensive process so if you’re using tutorial videos , watch them several times to be sure that you fully understand the process.

  1. First make sure that all of your PSS parts have arrived safely. Now remove the shaft coupling from the transmission output flange and then remove the shaft coupling from the shaft.
  2. Once removed, you’ll need to slide the shaft far enough to let you remove the old packing gland and the rubber hose that was attaching the packing gland. Now clean the exposed shaft with fine sandpaper. Be sure to pay attention to the keyway, which is at the forward end of the shaft. The stainless steel rotor will pass here, and any sharp edges could potentially damage the o-rings.
  3. Now slide the open end of the bellow and the hose clamps down the shaft and set it on the bare stem tube. Be sure the bellow is properly fitted over the shaft log. The bellow should overlap the stem tube by approximately the same amount as the bellow clamps. This will allow the hose clamps to tighten the bellow to the shaft log. Do not let the bellow slide too far down and over the stem tube. This could potentially damage the inner ribs of the bellow and limit its travel. Now tighten the hose clamps in order to secure the bellow to the stern tube. Carefully fit the black clamp protector to the tail of the hose clamps.
  4. Now return to the forward end of the bellow and gently place the carbon flange on that end, using the two hose clamps to secure it properly. Double check to confirm the flange is in excellent condition.
  5. Take out the stainless steel rotor and inspect it for imperfections. There should be two o-rings in the o-ring grooves inside the bore of the rotor. Check once more for any imperfections here. Take out two screws and gently thread them into the rotor holes. Stop just before they protrude inside the bore of the rotor. Set the remaining screws to the side.
  6. Grease the shaft and the o-rings of the rotor using dish soap or a water solution. Do NOT use oil, grease or silicon to lubricate. Slide the stainless steel rotor down the shaft.
  7. Re-attached the shaft coupling to the shaft. Be sure that all safety devices provided and recommended by the coupling manufacturer are in the correct place.
  8. Continue re-attaching, this time re-attach the shaft coupling to the transmission. Be careful to install it at manufacturer specifications. Once again, check for safety devices.
  9. Once the shaft is in place, check to make sure the carbon is perfectly centered on the shaft. The carbon ring will be bored at a larger diameter than the shaft. Be sure the bellow cuff is placed on the stern tube and the shaft is near the center in the shaft log. You can adjust the PSS so it runs true with the shaft. Now tighten all of the hose clamps around the stern tube and carbon.
  10. Now carefully slide the stainless steel rotor down so it gently touches the carbon. Use a marker or a piece of tape to mark this position as a “neutral” position.
  11. Sliding the stainless steel rotor aft, now compress the bellow by the proper amount, which should be indicated on the bellow compression chart. Use your “neutral” mark as a reference point. While keeping the bellow in the compressed position, tighten the two screws in the rotor using an allen wrench.
  12. Now take out two more screws and thread one into each of the rotor holes to further tighten them against the first set of screws. This will lock them in place.

Proper Maintenance

Like any other part of the boat, PSS Shaft Seals must be inspected regularly to insure they are in good condition, working properly and are not suffering from age, wear or chemical deterioration. PYI Inc. always recommends preventative maintenance to ensure the product’s quality remains intact. The company recommends replacing the PSS every six years or so to prevent unnecessary disruptions in your work. You may want to consider replacing o-rings and set screws in the stainless steel rotor, just to be on the safe side.

Maintenance kits are available for purchase if you plan on tackling this yourself. They include all of the items that will help you maintain your PSS until they need to be replaced, including a spare PSS bellow, two o-rings, five set screws, four brand new hose clams and an allen key. The kits can be ordered with any of the sizes you need.