# Main Water Shutoff Valve leak

**URL:** <https://boards.straightdope.com/t/main-water-shutoff-valve-leak/714935>\
**Category:** Factual Questions\
**Created:** [March 13, 2015, 9:17pm UTC](https://boards.straightdope.com/t/main-water-shutoff-valve-leak/714935 "2015-03-13T21:17:27Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![dougrb](https://avatars.discourse-cdn.com/v4/letter/d/76d3ee/32.png) [@dougrb](https://boards.straightdope.com/u/dougrb)\
**Post date:** [March 13, 2015, 9:17pm UTC](https://boards.straightdope.com/t/main-water-shutoff-valve-leak/714935/1 "2015-03-13T21:17:27Z")

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I have an old main water shutoff valve that developed a leak a week ago. There is a small knurled knob about 1/4" in diameter extending from the valve body about 1/2", 90 degrees from the actual shutoff knob. This knob has a small opening on the side where water was spraying out. As I rotate the knob with pliers this opening rotates. Different positions give various levels of spraying. One particular position reduced water flow to a dribble. I placed a cup underneath to catch the drip and was getting about a cup of water a day. It has now completely stopped. Does anyone know the purpose of this knob? I have looked at pics of shutoff valves and can’t find anything like it.

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**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\
**Post date:** [March 13, 2015, 10:02pm UTC](https://boards.straightdope.com/t/main-water-shutoff-valve-leak/714935/2 "2015-03-13T22:02:58Z")

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From your description it sounds like a bleeder valve to me.

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**Author:** ![boytyperanma](https://avatars.discourse-cdn.com/v4/letter/b/4491bb/32.png) [@boytyperanma](https://boards.straightdope.com/u/boytyperanma)\
**Post date:** [March 13, 2015, 10:08pm UTC](https://boards.straightdope.com/t/main-water-shutoff-valve-leak/714935/3 "2015-03-13T22:08:26Z")

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Look up ‘valve with waste port.’ The purpose of it is to be able to shut the valve off and use that port to drain the pipe beyond. Typically you’d use that style valve in places that get winterized.

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**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\
**Post date:** [March 13, 2015, 10:37pm UTC](https://boards.straightdope.com/t/main-water-shutoff-valve-leak/714935/4 "2015-03-13T22:37:23Z")

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yeah you might also hear it referred to as a shut off valve with drain back.

they are often with pipes serving outdoor hose bibs, to shut the outdoor faucet and drain the pipe beyond that to it.

in your case it might be to drain the house plumbing for an unheated freezing winter or plumbing work, though it would be slow to do so.

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**Author:** ![dougrb](https://avatars.discourse-cdn.com/v4/letter/d/76d3ee/32.png) [@dougrb](https://boards.straightdope.com/u/dougrb)\
**Post date:** [March 13, 2015, 11:18pm UTC](https://boards.straightdope.com/t/main-water-shutoff-valve-leak/714935/5 "2015-03-13T23:18:13Z")

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That’s it. Thanks for the help.