Ball valve

PabloPicasso

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Need to replace the toilet out ball valve as the handle turns but the valve is jammed shut. I have a couple of questions.

1. What chance have I got of opening the valve? Prizing the tubing off without may release a mess and if I can open the valve first and pump through it will be cleaner and less messy. Any suggestions of what to try?

2. It's a bronze thru-hull and bronze valve fitting. Should I replace with like for like, or a marleron plastic type.

3. How can I measure thread type before commencing the project, or will I need to get the valve off and take into a shop to ensure the correct size?

Anything else I'll need to consider with this job? The boat is on the hard until April.
 

prv

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1. Is the handle turning on the spindle, or the spindle turning and leaving the ball behind? In the former case you might be able to grip it with some mole grips or something; in the latter the only thing I can think of is to try to drift the ball around part-way with a slim chisel up the opening, which I doubt would be successful.

2. Up to you. Personally I’m happy with DZR brass.

3. The thread will be BSP and for a toilet outlet almost certainly 1-1/2. You can measure the outside of the valve and post it here for comparison if you think it might be something unusual like BSP 1-1/4 or BSP 2 - it’s not going to be a millimetre or two different.

Pete
 

Spyro

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1 little chance. The spindle is probably broken
2 I'd use the same type, they are easy to change and last long enough. Matelon are expensive
3 the size is usually stamped on them, for heads outlet it's probably 1 1/2 inch.

The plastic pipes are usually difficult to get off the hose tail. Cutting it is easy if you have extra to play with. Warming with a hairdryer helps also for putting on the hose on the new one.
 

PabloPicasso

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That all sounds useful. DZR with a stainless ball seems to be what is there. I'll see what prices are like.

What sort of sealant on the threads? Ptfe tape? Something else?
 

prv

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What sort of sealant on the threads? Ptfe tape? Something else?

PTFE is commonly used, including by me, though I understand it's a bodge really on the typically parallel-into-parallel thread arrangements found in yacht skin fittings.

I believe PTFE (trade name Teflon, after all) on threads is meant to reduce friction so that you can do up tapered threads tight enough to jam and seal. Parallel threads are meant to draw together two surfaces that then seal with a washer, gasket, or O-ring in between - there's not meant to be a fluid seal between the threads themselves. But the common yacht skin fitting with a ball valve perched on top (unlike the proper - expensive - hull-mounted seacock) doesn't provide any such sealing faces, and so we all merrily pack out the threads with PTFE or some other goo and it works perfectly fine at the low pressures involved.

Pete
 

Akestor

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That all sounds useful. DZR with a stainless ball seems to be what is there. I'll see what prices are like.

What sort of sealant on the threads? Ptfe tape? Something else?

Ι used polyurethane based sealant between seacock-fitting threads to be sure there will be no leacks. PTFE will not do the job as mentioned before. The boat is in the water or out?
 

rogerthebodger

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Need to replace the toilet out ball valve as the handle turns but the valve is jammed shut. I have a couple of questions.

1. What chance have I got of opening the valve? Prizing the tubing off without may release a mess and if I can open the valve first and pump through it will be cleaner and less messy. Any suggestions of what to try?

2. It's a bronze thru-hull and bronze valve fitting. Should I replace with like for like, or a marleron plastic type.

3. How can I measure thread type before commencing the project, or will I need to get the valve off and take into a shop to ensure the correct size?

Anything else I'll need to consider with this job? The boat is on the hard until April.

You need a 3 part type ball valve which makes servicing very easy.

triad_servicing.png


2366FT_2366FW.png
 

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Spyro

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Ι used polyurethane based sealant between seacock-fitting threads to be sure there will be no leacks. PTFE will not do the job as mentioned before. The boat is in the water or out?

PTFE tape will work fine if used correctly. I've replaced all my seacocks using ptfe tape and none have leaked.
 

Graham_Wright

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PTFE is commonly used, including by me, though I understand it's a bodge really on the typically parallel-into-parallel thread arrangements found in yacht skin fittings.

I believe PTFE (trade name Teflon, after all) on threads is meant to reduce friction so that you can do up tapered threads tight enough to jam and seal. Parallel threads are meant to draw together two surfaces that then seal with a washer, gasket, or O-ring in between - there's not meant to be a fluid seal between the threads themselves. But the common yacht skin fitting with a ball valve perched on top (unlike the proper - expensive - hull-mounted seacock) doesn't provide any such sealing faces, and so we all merrily pack out the threads with PTFE or some other goo and it works perfectly fine at the low pressures involved.

Pete

If you wind the tape on from the open end and gradually build up the layers, you can convert the parallel to pseudo tapered. I have just switched to the Loctite product (but that probably would not work to create a taper).
 

prv

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if that is a bodge, as you say, what is the correct way?

In engineering terms, either a tapered thread, which is designed to seal on the thread itself, or an assembly such that screwing the parallel threads together compresses a fibre washer, rubber gasket, or O ring between two flat faces.

This can't be done with the typical parts (generic ball valve, parallel-sided mushroom fitting, and whatever thin nuts you want to add) used to put together an adequate through-hull at a moderate price on a typical yacht. Which is why we all (myself very much included) bodge those parts together with tape or some other kind of sealant, and it's perfectly fine for the application.

Here's the proper seacock application that the mushroom fittings are actually intended for:

538a.jpg
s-l200.jpg


(It's an American drawing I found on Google, hence using their "National" threads instead of BSP)

Note that the mushroom's flange and the seacock body both seal onto the hull (if we consider the bonded-in backing block part of the hull) and that the thread mating doesn't need to be waterproof.

Note also that the hose barb in the drawing has a taper thread (NPT, vs NPS for "straight") to give a proper seal on that end of the assembly. The mushroom side has to be parallel because the point where it stops screwing in needs to be determined by the hull thickness, not by where the threads jam up.

Those flanged seacocks are rather more expensive than a plain ball valve, though.

Pete
 

prv

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How do you ensure the skin fitting does not move when you try to undo the valve fitting?

You can try gripping it with stilsons or oversized waterpump pliers, or have someone outside the hull hold it with the correct tool (forget the name) that engages on the lugs inside. But it's best to assume that it might move despite your best efforts and that you might need to rebed the skin fitting as well.

If you're dealing with old stuff it's often easier to just cut the flange off the outside of the skin fitting (it's easier than it sounds, there are a couple of tricks), tap the whole lot through into the boat, and replace with new, rather than trying to separate the pieces.

Pete
 

ghostlymoron

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I removed a gate valve from the skin fitting when I acquired Lapwing. I was careful not to move the skin fitting when fitting the replacement ball valve but on relaunching, there was a slight weep necessitating another haul out and rebedding the mushroom.
Most ball valves sold in chandlers are BSP tapered female threads which seal satisfactorily to the parallel threaded skin fitting using three turns of PTFE tape.
 

eilerts

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1. What chance have I got of opening the valve? Prizing the tubing off without may release a mess and if I can open the valve first and pump through it will be cleaner and less messy. Any suggestions of what to try?

I guess that if you take the handle off, you see the nut of the stuffing box of the spindle. Undo the nut and try to extract the spindle. The ball likely has a slot that the spindle goes into. Try to make a steel tool that can enter the slot and try to open the valve.
There is also an possibility that you can make the spindle grip the ball by giving it a knock with a hammer.

Another possibility is to drill a hole into the ball from the outside, just so that you move ball with a tool from the outside. Tape clear plastic bag around the through hull, with the tool inside - or watch where you are standing.

The former is kind of a long shot, but the latter is tested and worked (in my case)
 

prv

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A good facsimile of "the correct tool" (the name of which also escapes me) can easily be fabricated by cutting slots in a suitably-sized socket with an angle-grinder. Well worth having in stock.

Yep - I have a stack of ‘em strung on a loop of fence wire :)

Pete
 
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