Journey with Confidence RV GPS App RV Trip Planner RV LIFE Campground Reviews RV Maintenance Take a Speed Test Free 7 Day Trial ×
 

Go Back   Keystone RV Forums > Keystone Tech Forums > Keystone Questions
Click Here to Login

Reply
 
Thread Tools Display Modes
 
Old 04-01-2020, 09:34 AM   #1
Nomad44
Junior Member
 
Join Date: Mar 2020
Location: Atlanta
Posts: 11
Moving Black Tank Ventilation

Trailer: 2009 Passport 280BH

Goal: Remodeling bathroom and moving wall for more space in the bathroom

Problem: I moved my bathroom wall a few inches laterally. Previously the black tank vent stack ran up to the ceiling through the old wall. Now that I have moved it a few inches, if I ran the stack straight up again, it would be exposed in the middle of the bathroom, which is obviously not desired.

Questions: Has anyone drilled new ventilation holes into their black tank?
Can I use a smaller diameter pipe than the 1.5 in OEM size?
Can I just use some PEX or vinyl piping? This would allow me to have some bends and route under the flooring into the new wall location and back up.
Nomad44 is offline   Reply With Quote
Old 04-01-2020, 09:45 AM   #2
flybouy
Site Team
 
Join Date: Oct 2011
Location: Joppa, MD
Posts: 11,714
I would not go down is size or use any "flexible" tubing. The vent stack is sized to allow sufficient air into the tank when filling and draining the tank. Any added elbows or angled fittings will add restrictions to the airflow. Using any "flexible" material will run the danger of kinking in a bend and will not be able to support itself in a 8' vertical run.

The tank fittings are "spin welded" with a drill fitting. Moving the vent line I think would require dropping the tank to cap off the existing line and relocate it. If I'm wrong on this someone with more "hads on" experience please correct me.
__________________
Marshall
2012 Laredo 303 TG
2010 F250 LT Super Cab, long bed, 4X4, 6.4 Turbo Diesel
flybouy is online now   Reply With Quote
Old 04-01-2020, 10:49 AM   #3
Nomad44
Junior Member
 
Join Date: Mar 2020
Location: Atlanta
Posts: 11
Quote:
Originally Posted by flybouy View Post
I would not go down is size or use any "flexible" tubing. The vent stack is sized to allow sufficient air into the tank when filling and draining the tank. Any added elbows or angled fittings will add restrictions to the airflow. Using any "flexible" material will run the danger of kinking in a bend and will not be able to support itself in a 8' vertical run.

The tank fittings are "spin welded" with a drill fitting. Moving the vent line I think would require dropping the tank to cap off the existing line and relocate it. If I'm wrong on this someone with more "hads on" experience please correct me.
I'll provide some more context into this situation that may make a difference. I plan to marry my black and grey tanks. The gray tank will still have the original 1.5 in stack. I would imagine that there would be sufficient airflow with on 1.5 in stack on the orig gray tanks and lets say a 3/4 in stack on the black tank. I think this makes sense particularly if there are only liquids being emptied. I don't really care how long the dumping process would take and Pex piping could be used to prevent kinks in the hosing.

As far as dropping the tank is concerned, I had to replace some rotted flooring of the tank anyways so I have access to the top of the tank to the original black tank stack hole.

Not sure what "spin welding" is though.
Nomad44 is offline   Reply With Quote
Old 04-01-2020, 10:57 AM   #4
flybouy
Site Team
 
Join Date: Oct 2011
Location: Joppa, MD
Posts: 11,714
Quote:
Originally Posted by Nomad44 View Post
I'll provide some more context into this situation that may make a difference. I plan to marry my black and grey tanks. The gray tank will still have the original 1.5 in stack. I would imagine that there would be sufficient airflow with on 1.5 in stack on the orig gray tanks and lets say a 3/4 in stack on the black tank. I think this makes sense particularly if there are only liquids being emptied. I don't really care how long the dumping process would take and Pex piping could be used to prevent kinks in the hosing.

As far as dropping the tank is concerned, I had to replace some rotted flooring of the tank anyways so I have access to the top of the tank to the original black tank stack hole.

Not sure what "spin welding" is though.
The slower a tank drains the more solids will be left behind. Those solids can also be soap that settles out and collects on the bottom of a gray tank.
Google sin weld and you'll have plenty of reading material.
Good luck.
__________________
Marshall
2012 Laredo 303 TG
2010 F250 LT Super Cab, long bed, 4X4, 6.4 Turbo Diesel
flybouy is online now   Reply With Quote
Old 04-01-2020, 11:06 AM   #5
JRTJH
Site Team
 
JRTJH's Avatar
 
Join Date: Mar 2011
Location: Gaylord
Posts: 26,841
Quote:
Originally Posted by Nomad44 View Post
I'll provide some more context into this situation that may make a difference. I plan to marry my black and grey tanks. The gray tank will still have the original 1.5 in stack. I would imagine that there would be sufficient airflow with on 1.5 in stack on the orig gray tanks and lets say a 3/4 in stack on the black tank. I think this makes sense particularly if there are only liquids being emptied. I don't really care how long the dumping process would take and Pex piping could be used to prevent kinks in the hosing.

As far as dropping the tank is concerned, I had to replace some rotted flooring of the tank anyways so I have access to the top of the tank to the original black tank stack hole.

Not sure what "spin welding" is though.
If you have a 3/4" air inlet and a 3" valve outlet, if you pull the valve to empty the black tank, you won't get enough air flow through that 3/4" inlet. That will cause the outflow to slow (and gurgle) causing the solids to not flow out of the tank readily. Also, you stand a very good chance of collapsing the black tank from the "vacuum created by the rapid outflow and inadequate inflow"... If that happens a couple of times, you'll wind up with cracked corners on the black tank and need a replacement.

The size of the vent needs to be adequate to vent the tank being emptied. A 3/4" "reroute" from the black tank to the 1.5" gray tank stack will only provide 3/4" venting to the black tank, (about 25% of what's there with the 1.5" stack) and will probably damage your tank from collapse as well as not allow for adequate volume outflow, making a "thick solid layer" on the tank floor....

It would be much easier to hide the vent stack and much cheaper to use smaller materials at the factory... There's a reason all the manufacturers stick with 1.5" vent stacks rather than "downsize to cheaper, lighter and easier to use" smaller vents.
__________________
John



2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS
JRTJH is online now   Reply With Quote
Old 04-01-2020, 11:10 AM   #6
Nomad44
Junior Member
 
Join Date: Mar 2020
Location: Atlanta
Posts: 11
Good point on the solids and buildup. Has this become a serious issue with anyone in the past?

I'll try and do more research on airflow rates for 3/4 in piping and maybe even run a few tests on my own.

Ahh, I see what you mean by spin welding now. Is this the recommended method of attaching a fitting to the tanks if I were to make a new opening?
Nomad44 is offline   Reply With Quote
Old 04-01-2020, 11:15 AM   #7
Nomad44
Junior Member
 
Join Date: Mar 2020
Location: Atlanta
Posts: 11
Quote:
Originally Posted by JRTJH View Post
It would be much easier to hide the vent stack and much cheaper to use smaller materials at the factory... There's a reason all the manufacturers stick with 1.5" vent stacks rather than "downsize to cheaper, lighter and easier to use" smaller vents.
Very good points made all around. I will likely stick with 1.5 in piping.

In my case this would be drilling a new opening in the tank. I'm definitely open to this option, but any recommendations on a new fitting for the tank? As flybouy stated, the OEM "spin welds" the fittings on there. Would this be necessary? Can I just use plumbers cement?
Nomad44 is offline   Reply With Quote
Old 04-01-2020, 11:44 AM   #8
JRTJH
Site Team
 
JRTJH's Avatar
 
Join Date: Mar 2011
Location: Gaylord
Posts: 26,841
Have you considered a 45* fitting where the vent stack comes into the bathroom and a 45* fitting where it enters the wall? That would give you the option of "most or even all" of the exposed vent stack being "below the toilet level. It would be much simpler and probably look better to "box in a small bit" rather than "box in from floor to ceiling".... You might even find a route that would minimize almost all of the vent stack exposure by using two 90* fittings so the exposed part runs horizontal along the floor behind the toilet. Play with the options and see what you can come up with. There's lots of options that don't have "a bare pipe in the middle of the bathroom"....
__________________
John



2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS
JRTJH is online now   Reply With Quote
Old 04-01-2020, 07:15 PM   #9
Nomad44
Junior Member
 
Join Date: Mar 2020
Location: Atlanta
Posts: 11
Im think these are my best options now. I’ll try the two 90’s and see if I can squeeze that clearance out of the wall, I might have to get a little creative with my framing. Lol
Nomad44 is offline   Reply With Quote
Old 04-02-2020, 04:26 AM   #10
CedarCreekWoody
Senior Member
 
Join Date: Dec 2019
Location: Trinidad,TX
Posts: 968
Tank venting is perhaps even more important when flushing than when draining. When you flush there is a sudden in-rush of liquid and solids which will displace the air inside the tank. You want this air to quickly and easily flow up the vent pipe, not flow back out the toilet inlet and into the bathroom. For air to move easily and quickly it requires a large vent stack.
__________________
Woody
Cedar Creek Lake, Texas
2019 Laredo 290 SRL
2019 Ram 2500, 4x4, Cummins diesel
Andersen hitch
CedarCreekWoody is offline   Reply With Quote
Old 04-04-2020, 05:07 AM   #11
Nomad44
Junior Member
 
Join Date: Mar 2020
Location: Atlanta
Posts: 11
Quote:
Originally Posted by JRTJH View Post
If you have a 3/4" air inlet and a 3" valve outlet, if you pull the valve to empty the black tank, you won't get enough air flow through that 3/4" inlet. That will cause the outflow to slow (and gurgle) causing the solids to not flow out of the tank readily. Also, you stand a very good chance of collapsing the black tank from the "vacuum created by the rapid outflow and inadequate inflow"... If that happens a couple of times, you'll wind up with cracked corners on the black tank and need a replacement.

The size of the vent needs to be adequate to vent the tank being emptied. A 3/4" "reroute" from the black tank to the 1.5" gray tank stack will only provide 3/4" venting to the black tank, (about 25% of what's there with the 1.5" stack) and will probably damage your tank from collapse as well as not allow for adequate volume outflow, making a "thick solid layer" on the tank floor....

It would be much easier to hide the vent stack and much cheaper to use smaller materials at the factory... There's a reason all the manufacturers stick with 1.5" vent stacks rather than "downsize to cheaper, lighter and easier to use" smaller vents.
I found some information to some airflow calculations. Check this chart out.

For reference, I have a 30 gallon tank which comes to 4 cubic feet. At 3/4” the ventilation stack would be able to accommodate 10 cfm of airflow. This means approximately 5cf per 30 seconds. If I stepped up to 1” pipe I get 25cfm or 4cf in 10 seconds.

This all said, theses are free flow rates and not pressurized rates. It’s obvious that there will be some negative pressure generated. These flow rates rise very steeply at the beginning of their curve. See attached link for the curve. Keep in mind the it is a logarithmic scale.

https://base.imgix.net/files/base/ebm/hydraulicspneumatics/image/2006/09/hydraulicspneumatics_com_sites_hydraulicspneumatic s.com_files_uploads_custom_inline_archive_www.hydr aulicspneumatics.com_Content_Site200_eBooks_01_01_ 2006_Fig31png_00000014051.pngauto=format&fit=max&w =1440

https://www.engineeringtoolbox.com/docs/documents/1280/compressed-air-pipeline-capacity-liter.png
Nomad44 is offline   Reply With Quote
Old 04-04-2020, 06:00 AM   #12
KRumm
Senior Member
 
Join Date: Jul 2019
Location: Palm Springs
Posts: 122
Not all vent fittings are spun welded... Take a look at this video where a rubber gasket is used...

https://youtu.be/PQvtaBg0j_A
Attached Thumbnails
Click image for larger version

Name:	AC14A1B5-E42E-4BE9-8055-E292E39A866E.jpeg
Views:	252
Size:	390.3 KB
ID:	26062  
KRumm is offline   Reply With Quote
Old 04-04-2020, 06:51 AM   #13
flybouy
Site Team
 
Join Date: Oct 2011
Location: Joppa, MD
Posts: 11,714
Nomad44, what was the point of the last post? Are you justifying a 3/4" vent? The first link you posted doesn't work (at least for me) and the second is a chart that's more suited for pressurized lines. This is you're project so proceed as you wish, no need to justify to anyone. You asked for advice and some very knowledgeable people (some in the field of repairing RV's) have given their advice. I'll add this advice...if you are convinced that a 3/4" vent will work just fine then go for it but I'd advice against enclosing it all in and buttoning up the job before testing it. Good Luck!
__________________
Marshall
2012 Laredo 303 TG
2010 F250 LT Super Cab, long bed, 4X4, 6.4 Turbo Diesel
flybouy is online now   Reply With Quote
Old 04-04-2020, 07:09 AM   #14
flybouy
Site Team
 
Join Date: Oct 2011
Location: Joppa, MD
Posts: 11,714
Quote:
Originally Posted by KRumm View Post
Not all vent fittings are spun welded... Take a look at this video where a rubber gasket is used...

https://youtu.be/PQvtaBg0j_A
This is true for replacements. The OP want's to relocate his and as his is spun welded in place it's not a matter of unscrewing a fitting and screwing in a plug. He would need to cut the vent line and glue on a cap if there is sufficient room to do that below the floor, or remove the spin weld fitting and patch over the hole. The point was to make the OP aware that the fitting is a spin weld fitting and if went to "crank on it" with a pipe wrench to "unscrew" it he would most likely break the tank and render it useless. I don't recall anyone saying the OP "had to spinweld" in a new fitting. Hope this helps clarify.
__________________
Marshall
2012 Laredo 303 TG
2010 F250 LT Super Cab, long bed, 4X4, 6.4 Turbo Diesel
flybouy is online now   Reply With Quote
Old 04-12-2020, 08:07 AM   #15
Nagrompj
Member
 
Nagrompj's Avatar
 
Join Date: Mar 2013
Location: Pa
Posts: 75
Don’t forget, there may be a time when the only way the empty your tank is the honey wagon (vacuum truck.) Depending on the honey wagons vacuum even a 3” vent could be inadequate.
__________________
2013 Laredo 240MK
2008 F250 4x4 lariat 5.4
Nagrompj is offline   Reply With Quote
Old 04-13-2020, 08:21 AM   #16
CampNBrew2
Senior Member
 
Join Date: Aug 2018
Location: Vacaville
Posts: 306
How much room do you have between the floor and the top of the tank?

I'd use (2) 90s or (2) 45s to pipe it over to the new wall, even if- as John suggested- you need to build a small box over the joints.

Venting is as important as the drain. No way I would ever go smaller on the vent pipes. Unless you used a lot of them. It would take (4) 3/4" pipes to equal the area of the 1-1/2". But then you could not use them as a cleanout.

I have had good luck with Uniseal products (Compression fit tank adapter) but have never used them in a RV or mobile application (ie heavy jarring and vibration). Be sure and plug/seal your existing vent hole well.

https://www.google.com/search?q=unis...hrome&ie=UTF-8
__________________
2013 Premier 22RBPR
2022 GMC 2500HD 4x4 Gasser
2019 Beta 500 RR-s (Pasta Rocket!)
2015 Honda CRF250L (Wifes)
Camping, home brewing, and dirt bikes!
CampNBrew2 is offline   Reply With Quote
Reply

Tags
black tank, tank, vent

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

» Featured Campgrounds

Reviews provided by

Powered by vBadvanced CMPS v3.2.3
Disclaimer:

This website is not affiliated with or endorsed by the Keystone RV Company or any of its affiliates in any way. Keystone RV® is a registered trademark of the Keystone RV Company.


All times are GMT -8. The time now is 01:52 PM.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2024, vBulletin Solutions, Inc.