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Old 02-03-2004, 02:22 PM   #1
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Join Date: Oct 2003
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Repacing blackwater dump valve

I want to replace my Thetford blackwater dump valve because it is frozen in the closed position and I cannot unscrew the screws that hold its two pieces together. I tried the Screw-Out product from Sears but the rusted screws gave out. Drilling out the screws presents a bigger problem because of the heat produced and the subsequent melting of the valves plastic body around the screw holes.

As a side note, if you have a tail light assembly with rusted screws, use a drill to drill into the head of the screw and all of a sudden as the screw head heats up the plastic will begin to melt and the nasty old screw can be pulled out before the plastic cools and hardens once again!

I am thinking of cutting the pipe just above the valve and then replacing the frozen valve with a new valve. Is this a normal procedure?

If I cut the pipe, I think I will be left with a shorter than normal pipe on to which I need to cement the new valve. Would it be feasible to use a rubber sleeve that is made to join pipe sections to join an extension piece to which I cement the new valve?
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Old 02-03-2004, 02:40 PM   #2
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1978 31' Sovereign
Texas Airstream Harbor , Zavalla, in the Deep East Texas Piney Woods on Lake Sam Rayburn
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Can you cut em?


I replaced (rebuilt) my Thetford black water valve just this past weekend.

Just wondering;

1). Could you use a "Left Hand" (counterclockwise) drill bit?

2). How about a small Sawzall (Reciprocating Saw). I believe these can be rented, but they are not all that expensive to buy.
I think I have enough room to cut all four of the screws if I had to.

I ended up having to buy a whole valve ($45) because I could not find the "slide" separately.

I think that I would try to cut the four long screws, and back out the dutchmen with a vice-grip.

"Suck it up, spend the bucks, do it right the first time."

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Old 02-03-2004, 02:58 PM   #3
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Cutting the screw heads off may work


Your idea to saw off the screw heads is probably a good one. I've got to see how much working space exists in and around the pipes.

Of course, I might end up in the same situation as you and have to purchase the entire valve just to get the slide mechanism. If that is the case, perhaps I should just go ahead and cut off the valve and get it over with.

Thanks for you advice-I will let you know how things turn out.

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Old 02-03-2004, 04:20 PM   #4
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1956 22' Flying Cloud
Durango , Colorado
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I found the easiest thing to do is to cut both valves out and replace the whole thing. In my case (75 Tradewind) I could not easily replace just one valve.

So now I have new from the tanks to sewer connection. PVC is not that expensive....

Ken J.
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