Gate valve sizing

[Colin K]

Hello,
I have to replace two gate valves. They are imperial i know but not sure how to ascertain their sizes. Been told they are either 1 1/2" or 2" they are threaded each end and wondered if the size is across the opening? Or the size of the "gate" that slides? Anyone have any idea?
Cheers, Colin.

 

[VicS]

The BSP thread size.

the OD of 1½" BSP is 1.88", of 1¾" is 2.12" and of 2" BSP is 2.35"

 

[macd]

As Vic says, BSP thread size, which can be a bit confusing but is clearly explained on Wiki's page of the same name.

For most boaty applications, however, the correct size of gate valve is easily determined: it's tiny to the point of ceasing to exist. Calder will give a long list of reasons why ball valves are much preferred.

 

[Colin K]

Hello chaps,
Thanks for that, so if I take a micrometer across the threads I should be in the right ball game then I think? I am happy to stay with gate valves they are cockpit drains and have lasted 40+ years so cannot complain. The skin fittings ring nicely when I tap them so they are staying put so I was hoping just to change the whole gate valve or at least the guts of them.
Thanks again, Colin.

 

[macd]

Thanks for that, so if I take a micrometer across the threads I should be in the right ball game then I think? I am happy to stay with gate valves they are cockpit drains and have lasted 40+ years so cannot complain. The skin fittings ring nicely when I tap them so they are staying put so I was hoping just to change the whole gate valve or at least the guts of them.

A vernier is more than accurate enough.
The drawbacks of gate valves concern more than their durabiity, although most are made from plain brass which has well-known issues. Unlike ball-valves, it's impossible to see at a glance whether they're open or closed; they are prone to leaking due to trapping of debris under the gate; and the gate mechanism is physically less robust than a ball-valve's.

 

[Tranona]

Hello chaps,
Thanks for that, so if I take a micrometer across the threads I should be in the right ball game then I think? I am happy to stay with gate valves they are cockpit drains and have lasted 40+ years so cannot complain. The skin fittings ring nicely when I tap them so they are staying put so I was hoping just to change the whole gate valve or at least the guts of them.
Thanks again, Colin.

Replace them with DZR ball valves. Gate valves are not suitable for marine use - despite yours lasting so long. Beware of cheap gate valves as the fittings are brass even though the body may be bronze. All bronze valves are very expensive - roughly 50% more than functionally superior DZR ball valves.

 

[prv]

Thanks for that, so if I take a micrometer across the threads I should be in the right ball game then I think?

A ruler would do it . You don't need super accuracy to determine which of the few standard BSP sizes it matches.

Second the advice for a ball valve rather than a gate valve. I generally buy DZR from ASAP ( http://http://asap-supplies.com/ ) as most plumbers' merchants don't stock such large sizes, and chandleries can be unreliable about distinguishing between DZR and brass.

Pete

 

[Colin K]

Morning,
Thanks for the advise, New ball valves it is from ASAP ordered and on their way to me. 1 1/2" it was.

Cheers Colin.

 

[cryan]

There is nothing specifically wrong with gate valves. In some instances they can be safer as they can't be knocked open like a 1/4 turn ball v/v. The problems come with the materials used to construct them but the same could be said for any valve type. The other problem I see with gate valves is that people leave them open so that when they come to need to close them they are jammed up with corrosion or debris and won't move. If operated regularly and spindle threads are protected and lubricated they should last well and operate correctly.

*incidentally, vessels built under class conditions for Lloyds etc require ships side valves to be doubled and one of them must be a screw down type, normally a gate valve. The other is usually a butterfly valve to allow remote operation but there must be a manual gate valve as a back up which can be screwed down against the water pressure.*

 

[vyv_cox]

The biggest problem with gate valves is the lug used to open the gate is very small and can suffer dezincification. Closing the valve is rarely a problem, even when badly encrusted, as there is plenty of metal to push against. The problem comes when trying to open it again, when the lug can break off easily. Our water at home is very soft, another cause of dezincification, and we have had several gate valve failures of this type.