Drilling shallow holes for set screws for PSS shaft seal

slawosz

slawosz

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Hi,
in 'This old boat', Don Casey recommends drilling holes to make sure the steel rotor will be held in place. I wonder if someone actually did so? He gives an example of sunk yacht because the rotor slid on the shaft.
 
The grub screws have flame hardened tips that will easily penetrate the surface of a soft 300 series stainless steel shaft, provided they are tightened strongly enough and locked with the second set of screws. There might be a case to drill holes if the shaft was made from something else, e.g. a duplex stainless steel.

Some people put a hose clip on the shaft in case of rotor slippage. I do not, my PSS has been installed for 10 years or more, has had the rotor removed and reversed on the shaft but has not moved a millimetre in service.
 
vyv_cox said:
The grub screws have flame hardened tips that will easily penetrate the surface of a soft 300 series stainless steel shaft, provided they are tightened strongly enough and locked with the second set of screws. There might be a case to drill holes if the shaft was made from something else, e.g. a duplex stainless steel.

Some people put a hose clip on the shaft in case of rotor slippage. I do not, my PSS has been installed for 10 years or more, has had the rotor removed and reversed on the shaft but has not moved a millimetre in service.
Click to expand...

Seems like an endorsement for the PSS, I'm thinking about it!
 
Thank you. Providing I will get set maintenance screws with o-rings, can I simply remove rotor? I understand I should see marks on shafts?
 
vyv_cox said:
I am very happy with mine. I once had crevice corrosion on the stainless rotor face, details on my website, but since adopting the practice of fresh water flushing after haul out it has not recurred. That has been the only problem.
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What I found with my PSS seal was that the two faces would stick together if the engine wasn’t used for a couple of weeks. This caused some corrosion, as noted, but also put a lot of strain (in my opinion) on the bellows as the engine was put in gear and the faces unstuck. So much so, that I would pour fresh water over the seal if it had been left unused for a while to help unstick the faces before use. Perhaps the bellows were designed to cope with this, but I felt more comfortable soaking and unsticking them manually before use.
 
slawosz said:
Thank you. Providing I will get set maintenance screws with o-rings, can I simply remove rotor? I understand I should see marks on shafts?
Click to expand...
Yes, the rotor can be slid away from the bellows. Provided that the shaft is in good condition there should be little damage to the O-rings, although it is good practice to change them. Swapping over the inner and outer grub screws will give you an unused hardened point to reassemble. You will be able to see the old marks if the grub screw was tightened hard.
 
The grub screws may well have been supplied with hardened tips at one stage but this is no longer the case and AFAIK has not been for some years:


I refurbished mine 18 months ago and found no marks at all on the propshaft. If you are a cheapskate like me you can refashion the tips of the screws to avoid buying new, easy if you have access to a lathe. New ones may only be available UK as part of an expensive kit.
I found that the rotor has picked up some deposits on the face but was otherwise perfect, after c12 years use in our waters. After vyv_cox's warnings I now introduce some freshwater on lay up but only recently.

Years ago I experimented with trying to stick the mating faces of the seal with the boat laid up for winter. First I left the seal for 3 months then a further 2 months after drying the area with a hot air gun, did not succeed in getting much of a bond. Not to say it can't happen but I think the forces on the seal might be pretty low, as someone once said: "Seawater is an unlikely adhesive for carbon and stainless steel"

I use the Jubilee Clip method against slippage but place the clips a little behind the rotor so that any movement can be seen, I have never noticed any.

Face seals are used in all sorts of industries, if there were common problems it would be in the literature, it would be worth checking this our, I am sure vyv_cox has the full SP.

.
 
doug748 said:
Face seals are used in all sorts of industries, if there were common problems it would be in the literature, it would be worth checking this out, I am sure vyv_cox has the full SP.
Click to expand...
Your average refinery will have couple of thousand of them. Nowadays the only pumps that still have packed glands are fire pumps, as these will continue to operate, even if leaking, for longer surrounded by burning hydrocarbons.

Every other pump and most compressors will have mechanical seals. Sticking can be a problem in hot service where the product is viscous at ambient temperatures but there are generally flushing procedures for these. Sealed pressures can be considerable, certainly far greater than a few inches of seawater, but for very high figures the seals are balanced to have a smaller differential across the face.
 
slawosz said:
Hi,
in 'This old boat', Don Casey recommends drilling holes to make sure the steel rotor will be held in place. I wonder if someone actually did so? He gives an example of sunk yacht because the rotor slid on the shaft.
Click to expand...

I think it would be rather complicated to line up the rotor locking screws with those holes when the time comes to change the bellows (every 6 years is recommended) or when the seal is taken apart for other reasons. In which case you will have to drill new holes...
 
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