Momentum Grey tanks slow drain

[howson]

I think the recommended slope on drains is 1/4" per ft.

The GD DWV PLAN drawing for the 376THS states, Min. Grade 1/4" per foot but the note is associated with the washer, lav, and tub drains to the holding tanks, not the 3" and 1.5" drains from the holding tanks to the drain exit. Interestingly there's no criteria on the drawing for that (tank-to-drain) piping.

Makes sense, though, that without a proper slope gravity won't work. (Sometimes I amaze myself with the cosmic insights I post here...)

[gone AWOL]

Agreed, it's not a vent, or disk that was drilled and left inside.
i intentionally filled both grey tanks this morning (I was moving to another camp) so I needed to dump.
Trailer was auto levelled meaning, it was level....
Pulled grey 1... trickle, closed and then pulled grey 2... trickle.
Closed both, opened both, still a trickle.
Retracted my rear 4 jacks, rear end of the trailer dropped about 6"...they started to drain. They stopped draining after a while, the flow was better but nowhere near what it should be.
I then raised the front by about 12"....and low and behold, they started to flow again and drained.

This tells me the tanks are not installed so they can drain when on level ground.

Very disappointed because the fix will need to be very involved, ITS NOT A DUMP TRUCK GD, why do i have to have to deal with this after spending a boat load of money on something that is supposed superior to the competition???

Anyway, just another thing I'll need to do and spend money on to make what I bought work the way it was supposed to work.

I'm a construction guy, I'D LOVE TO BUILD THE CEO OF GD A HOUSE.....

[Cate&Rob]

So . . . we have gone AWOL with a 2022 Momentum 376 that won't drain properly and d2reid Dallas with a 2017 Momentum 376 where the tanks drain more-or-less normally. The obvious question is . . . what changed between 2017 and 2022? There is definitely not enough space in either 5th wheel to allow significantly different slope of the drain plumbing.

The tank drawing (provided to forum moderators) is dated 2017 so if this is the latest, there is no design change documented. It is quite likely that the gate valves changed from Valterra in 2017 to Bristol in 2022. (a supplier change across all Grand Design products in about 2019)

My "guess" is that although the handles are pulling about 3", they are not fully opening the gate valves . . . or there is a similar gate valve obstruction in both grey tanks. The only way to confirm this is by snaking a camera in through the drain, or dropping the coroplast and possibly removing the drain manifold for a detailed inspection.

BTW, I cut my 3" ABS drain manifold into three pieces (one for each gate valve) and reconnected these sections with hose clamped rubber connectors available at any plumbing store. This allows me to remove any single gate valve without loosening the others or shifting a tank. This has worked well.

Rob

[Jlawles2]

Cate&Rob Rob, valve not opening all the way is an interesting observation. How would raising the front of the unit to the extremes mentioned increase water flow to normal with a partial open valve (I do understand the variable opening in the gate at partial open)? I'd suspect that water flow to decrease over drain time if the valve was not opening all the way.

One other thing to check, this requires dropping the coroplast, is to check that the drain lines are straight and do not have a sag or hump. Either of these could cause drain performance issues. Particularly a hump in the line causes something called the "waterfall" effect. https://www.youtube.com/watch?v=zdkp9N3qfkI Grady does a nice job of explaining things with his clear pipe.

[Cate&Rob]

Jlawles2 Hi Joseph,

Tipping the entire RV raises the tank relative to the outlet. This increases the the water "pressure" (due to gravity) to force more liquid through the smaller "hole" created by a partially open gate valve. Think of the flow out of a water bottle held horizontally or tipped down towards the opening.

This does raise another thought . . . if the vent pipe is too far into the tank and covered by liquid, air can't get into the tank to allow the liquid to flow out. Possible but unlikely to be the same configuration in two different tanks and the AAVs should provide a source of replacement air during draining, even if the tank vent is covered. This situation would allow a significant increase in flow volume towards the end of the draining as the vent is uncovered. This has not been mentioned.

In my Reflection 303, the drain manifold is almost horizontal. I still get a rush of water as soon as the gate valve is opened, even from the galley grey tank which is draining through a 1 1/2" gate valve. I don't think drain manifold slope is the problem.

Rob

[Country Campers]

I would guess that raising the front of the RV may help but, the tanks on this model are oriented so that the drain is towards the frame or drivers side of the RV so raising the front would only move the contents to the rear or side of the tank and not totally towards the drain. To accomplish this one would have to raise the door side of the RV to move the contents towards the drain outlet of the tank. The tank drain is located on the end of the tank at the center.

Brian

[gone AWOL]

So . . . we have gone AWOL with a 2022 Momentum 376 that won't drain properly and d2reid Dallas with a 2017 Momentum 376 where the tanks drain more-or-less normally. The obvious question is . . . what changed between 2017 and 2022? There is definitely not enough space in either 5th wheel to allow significantly different slope of the drain plumbing.

The tank drawing (provided to forum moderators) is dated 2017 so if this is the latest, there is no design change documented. It is quite likely that the gate valves changed from Valterra in 2017 to Bristol in 2022. (a supplier change across all Grand Design products in about 2019)

My "guess" is that although the handles are pulling about 3", they are not fully opening the gate valves . . . or there is a similar gate valve obstruction in both grey tanks. The only way to confirm this is by snaking a camera in through the drain, or dropping the coroplast and possibly removing the drain manifold for a detailed inspection.

BTW, I cut my 3" ABS drain manifold into three pieces (one for each gate valve) and reconnected these sections with hose clamped rubber connectors available at any plumbing store. This allows me to remove any single gate valve without loosening the others or shifting a tank. This has worked well.

Rob

What changed was the floorplan, well somewhat, as such i suspect things in the underbelly could have been moved around too.
main changes are:
Entry door moved about 10' back.
Slides are now smaller in the living room.
Kitchen is bigger, bigger slide.
Kitchen layout changed.
Dining room slide is bigger.

The changes to slides might have necessitated moving tanks around. Just my theory....

Again, don't tell me these things go through a QC process before leaving the factory, I don't buy it, too many obvious mistakes or blatant workmanship issues.

Our small pelmet in the hallway fell off yesterday, the 2 little screws came right out of the wall, yes two screws holding up the pelmet with roller blind. There is 4 holes in the bracket ...go figure. But I bet you they managed to get an extra unit out that day .....
(It's high up under the roof, no one bumped it)

.....just venting.

[howson]

Jlawles2 This does raise another thought . . . if the vent pipe is too far into the tank and covered by liquid, air can't get into the tank to allow the liquid to flow out.

Rob--could your hypothesis be tested by opening faucets (with water off, obviously) providing another source for air to enter the tanks?

gone AWOL -- does the black tank drain as expected? (It uses the same main external drain as the grays but has a 3" pipe coming out of the tank.)

I ask because there is a difference in how the tanks are connected to the main external drain. GD uses a 1.5" pipe for the gray and a 3" pipe for the black. (Why there's a 1.5" adapter on the exact same model tank as the black I can't explain.)

I'm just spit-balling and could be wrong, but with the tanks installed side-by-side it doesn't make sense to me that the black is sloped correctly (assuming it drains as expected) but the grays are not installed correctly. If the drawing and parts lookup site are correct all three tanks are the exact same model. (I sent a request to GD for more information on the tank. I'll post here when I get a response.)

Howard

[Cate&Rob]

gone AWOL
Unless the location of the bathroom or the kitchen island have changed, I doubt that the location of the tanks would have moved. The latest holding tank layout that I can find (dated 2019) shows the black tank under the toilet, the bathroom grey under the bathroom vanity and the galley grey just forward of that. As Country Campers Brian notes, all tanks drain towards the left (street) side, so tipping the trailer fore/aft should have minimal affect. With the gate valves along the inside of the left frame rail, you should be able to unfasten a section of underbelly coroplast enough to see if the gates are opening the full 3" when the cable is pulled.

howson Howard, the water pressure system is entirely separate from the drain system . . . I am not sure where you are going with the idea of opening the faucets.

Some trailers have 1 1/2" gate valves on some of the grey tanks, but I have no idea why. My Reflection 303 has one 3" and one 1 1/2". I have seen other 303s with all 3" gate valves. In any case, I still get an initial rush of water when opening the 1 1/2" gate.

Rob

[Country Campers]

gone AWOL

I would think that you RV is new enough that it should still be under warranty. Have you contacted your selling dealer to get his issue resolved?

Brian

[howson]

Howard, the water pressure system is entirely separate from the drain system . . . I am not sure where you are going with the idea of opening the faucets.

Duh...senior moment.

[Jlawles2]

Cate&Rob Rob, understand pressure concept (hated fluid dynamics). Based on the description, it almost sounds like the drain outlet for the grey tanks is below the line.

It would be interesting to have someone scope the line to see the position of the valve at full open.

[gone AWOL]

Rob--could your hypothesis be tested by opening faucets (with water off, obviously) providing another source for air to enter the tanks?

gone AWOL -- does the black tank drain as expected? (It uses the same main external drain as the grays but has a 3" pipe coming out of the tank.)

I ask because there is a difference in how the tanks are connected to the main external drain. GD uses a 1.5" pipe for the gray and a 3" pipe for the black. (Why there's a 1.5" adapter on the exact same model tank as the black I can't explain.)

I'm just spit-balling and could be wrong, but with the tanks installed side-by-side it doesn't make sense to me that the black is sloped correctly (assuming it drains as expected) but the grays are not installed correctly. If the drawing and parts lookup site are correct all three tanks are the exact same model. (I sent a request to GD for more information on the tank. I'll post here when I get a response.)

Howard

Yeah no problem with the black at all.

[gone AWOL]

gone AWOL

I would think that you RV is new enough that it should still be under warranty. Have you contacted your selling dealer to get his issue resolved?

Brian

I am 53, I honestly don't think I have enough years left for the dealership to fix this.....

Dealerships replace awning caps, door clips, latches etc....they don't fix complex engineering issues. In my experience they replace stuff but do not deviate from the original.

(Warranty is a acronym for "please sign here and once we have your money bugger off")
I always get a story when it comes to warranty.....

I am not even going down that warranty road because we fulltime and I can't afford 9 months of hotel stay.

If it was fixable, GD would have done it right the first time, right?

[howson]

gone AWOL


GD's parts department responded to my inquiry. The tanks in your Momentum are made by Alpha Systems. On the Alpha website the product is found by quering for product 466RAW. The drawing is here: https://alphallc.us/wp-content/uploads/466001.jpg

When able, please peek under the coroplast of your Momentum to see if the three tanks are indeed the same model. Again, the only difference you should find between the gray and black tank installation is the grays will have a 1.5" adapter glued onto the tank's exit. (It will be next to impossible to convert the original grays back to 3" if your tanks are assembled like those on my 315RLTS.)

The smaller 1.5" exit on the gray tanks could explain why, if there is construction debris in those tanks, that the black still drains OK but the grays do not. When you raise the trailer nose-high the debris fall to the aft side of the tank as that now becomes the low point in the tank. (That's just a guess.)

Regarding your comments about warranties, dealer repairs, and "doing it right the first time"...no argument from me, but since we can't do anything about that (other than not buy an RV from any manufacturer) now you know the reason for this forum as envisioned by TucsonJim and Owners-helping-owners fix (and modify) their RV. Oh, and helping Yoda spend money on tools is also now a formal goal of the forum, too. (Inside joke...Keith won't mind!)