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Wednesday, January 18, 2012

RV Dump Valve Positioning

I saw your video about electric Drain Master Valves on the Drain Master web site.  I noticed that in your demo, the valve was installed in a vertical position.  I already have electric valves on my Beaver Patriot Thunder but the plumbing was done such that the valves are in the horizontal position.  Do you think installing the Drain Master Valve in a horizontal position will be a problem? Dick Y., (Enid, OK)

Indeed, Drainmaster and I both recommend that any termination valve be positioned with the valve body facing upward, Dick; or as upward as possible. Here’s why. That portion of the valve body is simply a cavity between the two halves of the valve where the actual “gate” portion will slide into during evacuations. When the valve is in the closed position, it’s just an empty void. If you look at a common termination valve when it is open, (obviously after you’ve dumped the tank!), you’ll notice the two seals on either side of the gate never completely close against each other. They are there to keep the gate from leaking when the valve is closed. They only make contact with the gate. With that open seam between the two seal rings when the valve is opened during draining of the tank, liquids, tissue and waste can migrate into that void if the valve is positioned horizontally or downward. If the valve body is positioned upwards, gravity will prevent that void from filling during evacuations.

However, your coach, with its bottom-draining holding tank is a little different. As you are aware, on the Patriot Thunder, the valve is positioned flat and mounted directly to the bottom of the holding tank, so your only optional positioning of the valve is in a 360-degree circular fashion. The valve will always remain flat. One problem with the design of your plumbing bay is that the holding tank was not supported properly and it had a tendency to warp during the process of filling the holding tank. This warpage as the tank fills causes stress on the fitting, the valve and all the plumbing downstream. In some cases, the bottom of the tank (and the installed termination valve), may actually be skewered a bit and not totally flat.

If it’s not possible to rework (to some degree of difficulty), the existing waste plumbing fittings and piping to accommodate a new valve in the “body up” position, your best bet is to see if the fitting that is welded into the bottom of the tank leans to any particular direction. If you can see it with your naked eye, then try to install the new Drainmaster valve with the body turned toward the highest point. It won’t be much, but it just may be enough to keep moisture and contaminants from gaining access to that void in the body of the valve.

Since gravity is your friend when draining the holding tank, it will likely drain quickly through that bottom outlet and pass through the valve before it readily has a chance to gather moisture and waste remnants. Horizontal tank outlets are more prone to that problem. Another good thing in your favor; the Drainmaster electric gate valve is now constructed with new, precision-fit stainless steel gears and any intrusion of moisture in the gearbox will likely have no affect in the long run anyway. I think you’ll be fine just replacing the existing valve with the Drainmaster. It might also be a good idea to add additional support for that shelf the holding tank sits on. I think a couple short sections of 2X4 wedged between the bottom of the plumbing bay and the bottom of the holding tank shelf should help keep the tank from flexing and warping during the time it is being filled.


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