Black water tank flush line pressure

I think you may want to invest in a pressure control device that is used exclusively for the black tank spray.  Your observation that the pressure should not be too high is something that many of us may not have thought about, but should have.  I've never used a pressure control device for the black tank spray, but as I think about your practice, I am realizing that I should have.  There are some pump out fresh water faucets that have some pretty high pressure water that could blow the plumbing apart.  Thanks for sharing your concern.

Hello Tulefrog!

A good question. After thinking about it, and how the system works it is my thought that it wouldn't need a pressure reducer....unlike the rest of the H2O systems in our trailers. And keep in mind there are different types of "water pressure regulators".

The most common type of regulatory used is the simple brass type with a fixed restrictor inside. (I broached this topic last week, I think). I believe they only control water pressure while the water is actually flowing through it (simple hydraulics in action). The second you close the tap in your trailer all water on both sides of the brass regulator will stop moving and the pressure will equalize, potentially over pressurizing the entire water system and could lead to leaks.

The 2nd type is the one I upgraded to, where it is attached to the faucet at the post, has an adjustment screw and a guage built into it, and you adjust what you want the pressure reaching your trailer will be. I think mine is set to 45 psi but would need to check to make sure. This is the only one that actually protects you from over pressurization of your trailer water system.

Now let's look at your black tank flush. You have to drain your black tank first and leave the tanks gate valve open to prevent the pressurized water coming in from over pressurizing the tank itself...you don't want to trap the air in the tank as you use your black tank flush as something would give (edit begins here)if your black tank vent is plugged or otherwise restricted from working properly. I would guess it would be your toilet seal in the bathroom if your vent syack is plugged...mental image of Old Faithful... Not good if that happened, we can all agree.(end of edit)

So, the gate valve is open, removing the tank over pressurization concerns. You attach your hose that you only use for flushing your black tank (we use an orange one, can't mistake it!), turn on the water and hear the nozzle spraying water around inside the tank and washing it out. At no time are you shutting the water off in your trailer, as you can't if the system is installed correctly.

My conclusion is that you won't/can't damage your black tank wash system if it is working properly even if water pressure is a bit high as you are letting it flow through the sprayer so it would never reach its full (potentially damaging) pressure.

This is the difference between the 2 systems. Your normal water system in your trailer is normally turned off and therefore subject to potential over pressurization damage if you don't have the "proper" water pressure controller (see beginning of this post).

If still concerned about it, by all means get one of the cheaper brass fixed water pressure controllers and use it only with your black tank flush...leave it attached to the orange hose so it doesn't get used for anything else. And then go and get the slightly more expensive adjustable water pressure controller that are available and protect you whole trailers water system!

My 2 cents on this interesting topic. (1.5 American cents ;-)

Have a great day,

Andy

Thanks for the reminder that there is a vent StephenH...but as you say, a stinky fountain of any sort is a bad thing!

Andy

I don't think it would be overflow initially, until the tank was physically filled with water. It would start as more of an....ummm....dirty brown misty cloud and build up from there.

Of course this is just conjecture...please make sure this never happens by leaving your black tank gate valve open till completely finished draining and theblack tank flush water line is turned off and disconnected.

Why does the Robin Williams movie "RV" come to mind.

Andy

I wonder how well the sprinkler orifice is connected to the waterline.  It has to restrict flow in order to create a spray.  Some pump out stations I've been to have some pretty serious water pressure that conceivably could put enough pressure in the line that the sprinkler head may not be able to accommodate it.  Knowing the cheap materials and sloppy plumbing work done by FR, I think it may be the better part of discretion not to over pressurize the line, but I could just be paranoid.