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Old 15-04-2015, 16:08   #1
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Stuffing box gland designs

Hi all,

Our traditional stuffing box assembly looks bad and needs replacement. We were looking at shaft seals, and besides controversial opinions we don't have enough shaft space for those (a dry bilge would have been nice on a steel boat).

The one installed now is plastic and the previous owners told us to tighten the gland when docked to stop water from entering and loosen it again when cruising. Besides not knowing how good that is for the stuffing box, it's kind of hard for me to judge how much water/ drips per minute etc. is appropriate. Advice on that would be nice, i.e. how concerned do I need to be?

What I was mainly wondering, though, is if we should change the actual gland together with packing and hose. Does it matter if it's plastic or any other material? I read about ones with a grease insertion point. In which ways are these better/ worse? Do they use the same packing material? Any other considerations?

Thanks for sharing your experience!

Cheers,
Phil
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Old 17-04-2015, 23:47   #2
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Re: Stuffing box gland designs

If you have a steel hull, any other metal stuffing box will have to be protected with a zinc. That maybe why it's plastic.
The drips of water lubricate the shaft. You only need a few drops a minute. When you tighten down to stop the drips, you stop lubrication. If you run that way your shaft will heat up and wear. Eventually the shaft will have to be repaired or replaced.
My old commercial fishing boat had twin greaseable stuffing boxes. When I bought the boat I replaced the old packing and adjusted for a slight drip. Then greased it (waterproof grease). With the grease, it didn't drip or warm up. The water pressure seemed to keep the grease in contact with the packing and shaft. About once a month I gave each fitting a single pump from a grease gun I kept with waterproof grease. Every couple years I opened up the stuffing box and pulled the packing and scraped out the grease. I didn't need to. Everything was always ok. I reused the packing. I never had to adjust the packing after the initial setup.
You can drill a greaseless stuffing box, but need to get the grease to deposit at the edge of the packing, not on top of the packing.
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Old 19-04-2015, 04:00   #3
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Re: Stuffing box gland designs

Thanks, Lepke, for sharing your experience. After measuring and shopping around I came to the conclusion of keeping our old plastic gland - the greasable ones (and everything else for that matter) I could find were all too long for our shaft space. The one we have now is about 2cm long after the hose, and there's only about 2 more cm until the shaft coupling. The tool we use for tightening is made of a rolled steel plate so that it can grip the narrow bolt head.

It does work fine so far, it's just a bit annoying having to tighten it while docking to prevent water from coming in plus I was concerned about its reliability. As you mentioned, the material might be of importance since everything will be submerged in sea water inside the hose. Plastic might be good since the moving parts will not corrode together, but might melt if the water flow is too low.

So, I'll just exchange the old hose and the stuffing material and make sure that we don't forget to adjust the water flow to a drop per minute when heading off. And maybe I can find a plastic container to fit under it to collect the water.

Cheers,
Phil
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Old 19-04-2015, 11:11   #4
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Re: Stuffing box gland designs

A well adjusted stuffing box will leak bit when running but not when stopped. You should check and maybe replace your stuffing if you cannot adjust to achieve this.

You can also switch to GFO dripless packing which works well:

GFO Packing | SG Group Div of MGP Systems Inc.
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Old 20-04-2015, 00:54   #5
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Re: Stuffing box gland designs

Quote:
Originally Posted by Xlantic View Post
A well adjusted stuffing box will leak bit when running but not when stopped. You should check and maybe replace your stuffing if you cannot adjust to achieve this.

You can also switch to GFO dripless packing which works well:

GFO Packing | SG Group Div of MGP Systems Inc.
Thanks for the tip. I will definitely change the packing soon. The GFO packing material sounds like a wonder product, I will check it out and see if it's available in Scandinavia.

Cheers,
Phil
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