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06-11-2018, 05:18 PM
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#21
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Senior Member
Join Date: Jun 2012
Posts: 10,907
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Ok, here's the air pressure side:
Solve for increase in air pressure due to temperature increase only
Assume:
Volume is constant for temperature increase Then Ideal gas law for this case: P1/T1=P2/T2 Assume:
Air pressure started at 15 psig at 60 deg (P1) Solve for air pressure at 130 deg (P2) Since T is in terms of absolute temperature:
T1 = 460 + 60 = 520 deg T2 = 460 + 130 = 590 deg Then P2 = P1T1/T2 = 15 x 590/520 = 17.019 psig
Now, solve for increase in pressure due to expansion of water by 1/8 inch
1/8 in = 0.125 inch = 0.010416 ft Assume:
Initial air volume (V1) is 1 sq ft by 3/4” high Then:
V1 = 1 sq ft x [.75 inch x 1 ft/12 inch] = 0.0625 cu ft. Since the water level increase was 0.010416 ft, then final volume of air would be:
V2 = 0.0625 cu ft – [0.010416 ft x 1 sq ft] = 0.052084 cu ft Then:
The ideal gas law for this case: P1V1 = P2V2 So:
P2 = P1V1/V2 = 17.019 psig x 0.0625 cu ft/0.52084 cu ft = 20.4225 psig So pressure increase is about 20 psig just heating the water/air pocket from 60 to 130 deg F. Nothing like 150 psig. Even if you added 60 psig from your city water connection.
(I think I should have called the pressure units PSIA rather than PSIG, but it's been a few years since I've done this.)
__________________
1988 Coleman Sequoia - popup (1987-2009) - outlasted 3 Dodge Grand Caravans!
2012 Roo19 - hybrid (2012-2015)
2016 Mini Lite 2503S - tt (2015 - ???)
2011 Traverse LT, 3.6L, FWD
2009 Silverado 1500 Ext Cab, 5.3L, 4x4, 3.73
2016 Silverado 2500HD Dbl Cab, 6.0L 4x4, 4.10
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06-11-2018, 05:24 PM
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#22
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Senior Member
Join Date: Jul 2017
Posts: 4,056
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Quote:
Originally Posted by nomad297
You’re probably not a plumber, so you may not notice the things a plumber will notice. I’m sure I wouldn’t notice some things that you would in your line of expertise, but I would believe what you told me.
How many beers do you have?
Bruce
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I am a plumber and a rv owner for many years and i doubt very much any pressure ever gets close to 150psi . i have never noticed any build up of pressure in my unit , ever and that 3yrs full time . from Florida to Montana. the PRV would pop off constantly at those pressures not just drip . I think someone is over thinking what goes on in there H/W/H
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06-11-2018, 05:29 PM
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#23
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Senior Member
Join Date: Jul 2015
Posts: 7,053
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Quote:
Originally Posted by rockfordroo
Ok, here's the air pressure side:
Solve for increase in air pressure due to temperature increase only
Assume:
Volume is constant for temperature increase Then Ideal gas law for this case: P1/T1=P2/T2 Assume:
Air pressure started at 15 psig at 60 deg (P1) Solve for air pressure at 130 deg (P2) Since T is in terms of absolute temperature:
T1 = 460 + 60 = 520 deg T2 = 460 + 130 = 590 deg Then P2 = P1T1/T2 = 15 x 590/520 = 17.019 psig
Now, solve for increase in pressure due to expansion of water by 1/8 inch
1/8 in = 0.125 inch = 0.010416 ft Assume:
Initial air volume (V1) is 1 sq ft by 3/4” high Then:
V1 = 1 sq ft x [.75 inch x 1 ft/12 inch] = 0.0625 cu ft. Since the water level increase was 0.010416 ft, then final volume of air would be:
V2 = 0.0625 cu ft – [0.010416 ft x 1 sq ft] = 0.052084 cu ft Then:
The ideal gas law for this case: P1V1 = P2V2 So:
P2 = P1V1/V2 = 17.019 psig x 0.0625 cu ft/0.52084 cu ft = 20.4225 psig So pressure increase is about 20 psig just heating the water/air pocket from 60 to 130 deg F. Nothing like 150 psig. Even if you added 60 psig from your city water connection.
(I think I should have called the pressure units PSIA rather than PSIG, but it's been a few years since I've done this.)
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What “air pocket”? Where have you even considered an absolute volume for an “air pocket”?
I will put my plumbing experience up against your flawed math any day.
Bruce
__________________
2016 Rockwood Windjammer 3029W Diamond Edition
2015 Chevy 3500HD LTZ 6.0 Crew Cab 4x4 Long Bed 4.10:1 SRW
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06-11-2018, 05:32 PM
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#24
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Senior Member
Join Date: Jul 2009
Location: Warsaw,NC
Posts: 7,184
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I brought a case of wine from my local winery, about $5.50 a bottle, Memorial Day special. I opened a bottle tonight and since I have a small brain like a chicken, I drank half a bottle and I’m corked, so y’all have a good night and I’ll think about this some more tomorrow or hopefully never
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06-11-2018, 05:35 PM
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#25
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Senior Member
Join Date: Jun 2012
Posts: 10,907
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Quote:
Originally Posted by nomad297
What “air pocket”? Where have you even considered an absolute volume for an “air pocket”?
I will put my plumbing experience up against your flawed math any day.
Bruce
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The 2nd half of my second post addresses the air pocket (see V1 and V2).
There is a device inside the water heater that creates the water pocket. Pic below. It is installed with the end pointing down. I believe it will give you AT least 3/4 inch.
I have ASSUMED 1 sq ft as a surface area. I think this is pretty close to the surface area in my Suburban, but even if it's only 0.75 sq ft, it isn't going to make that much difference in my calculations (you can change it and run through them yourself). I gave them 3/4 inch for the air pocket based on the pic below. If you don't like 3/4 inch, use 1/2 inch. Again it won't get you close to 150 psig. But I suspect the air pocket is greater than 3/4 inch.
Of course some of this air will dissolve into the water, allowing the air pocket to decrease in size, which is why you were told you should open the PT valve every few days.
__________________
1988 Coleman Sequoia - popup (1987-2009) - outlasted 3 Dodge Grand Caravans!
2012 Roo19 - hybrid (2012-2015)
2016 Mini Lite 2503S - tt (2015 - ???)
2011 Traverse LT, 3.6L, FWD
2009 Silverado 1500 Ext Cab, 5.3L, 4x4, 3.73
2016 Silverado 2500HD Dbl Cab, 6.0L 4x4, 4.10
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06-11-2018, 05:40 PM
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#26
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Senior Member
Join Date: Sep 2009
Location: Lexington, NC
Posts: 2,621
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Who cares?
__________________
2018 Coachmen Apex 249 RBS
2010 Silverado LT 5.3 V8
The world is a great book, of which those who never stir from home
read only a page. - St. Augustine
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06-11-2018, 05:42 PM
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#27
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Senior Member
Join Date: Jul 2015
Posts: 7,053
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Quote:
Originally Posted by MR.M
I am a plumber and a rv owner for many years and i doubt very much any pressure ever gets close to 150psi . i have never noticed any build up of pressure in my unit , ever and that 3yrs full time . from Florida to Montana. the PRV would pop off constantly at those pressures not just drip . I think someone is over thinking what goes on in there H/W/H
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What kind of plumber are you? To most plumbers a PRV is a Pressure Regulating Valve, more commonly referred to as a Pressure Reducing Valve. If you are referring to a Temperature and Pressure Relief Valve, most plumbers refer to them simply as a T&P. And I don’t know any plumbers who refer to a water heater as a H/W/H — a Hot Water Heater? No. We just refer to them as Water Heaters.
Again, what are your credentials?
Bruce
__________________
2016 Rockwood Windjammer 3029W Diamond Edition
2015 Chevy 3500HD LTZ 6.0 Crew Cab 4x4 Long Bed 4.10:1 SRW
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06-11-2018, 05:57 PM
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#28
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Senior Member
Join Date: Jun 2013
Location: Between Pickles Gap and Toad Suck, AR
Posts: 6,070
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I am not a plumber.
I am a showerer.
I want all the pressure I can get. So far, nothing has burst. I have some number of psi of pressure, I'm very sure. Sorta like blood pressure..........over zero is good.
__________________
"Next to prayer, fishing is the most personal relationship of man" Herbert Hoover
"American by Birth, Southern by the Grace of God"Lewis Grizzard
FROG AR-0019-242
2016 GMC Denali 3500Dually--2017 CC 36CKTS
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06-11-2018, 06:02 PM
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#29
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Senior Member
Join Date: Mar 2009
Location: Baltimore Md.
Posts: 122
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Just a quick check on PEX website their tubing is not good for 150 psi. Their chart shows 100 psi@110 degrees. Also that hose from the campground bib to your camper is no good for 150 psi.
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06-11-2018, 06:03 PM
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#30
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Senior Member
Join Date: Feb 2015
Location: Southern, IL
Posts: 3,272
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I go to the shower house. I do not want to hear it from my DW about any mess I may leave behind. LOL...
__________________
Bob & Michelle
2016 Ford F-250 Lariat 4x4
2017 Flagstaff Super Lite 526RLWS
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06-11-2018, 06:31 PM
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#31
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Senior Member
Join Date: Jul 2017
Posts: 327
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Papa Roo beet me to spec for PEX, which I believe is the plumbing used in most RVs these days but I'll post the expanded version for the sake of argument:
"Uponor PEX tubing carries the following hydrostatic temperature and pressure ratings.
200°F (93.3°C) at 80 psi
180°F (82.2°C) at 100 psi
120°F (48.9°C) at 130 psi (½" piping only)
73.4°F (23°C) at 160 psi
In accordance with ASTM F876 Standard Specification for Cross-linked Polyethylene (PEX) Piping, the excessive temperature and pressure capability for Uponor AquaPEX® is 210°F (99°C) at 150 psi."
Respectfully Nomad while I do agree pressure increases with temperature your 150 psi estimate is quite a bit too high. I'd like to refer you to the following website (there are many others as well). https://www.inspectapedia.com/plumbi..._Expansion.php
You'll note the following at this site which has been my general experience as well; " As a point of reference, in a residential hydronic heating boiler we actually observe an internal water pressure rise from 12 psi cold up to 28 psi hot as the boiler temperature increases from perhaps 60 °F up to 180 °F.
(This is much hotter than we should ever see in a domestic water heater tank where to avoid scalding hazards we limit water to about 100 °F. With a mixing valve or tempering valve installed we still limit water heater temperature to around 120 °F.)"
A real world increase in a RV would be about a 5 - 12 psi increase depending on the temp of the initial cold water being raised.
__________________
_________________________
Crusader 337QBH
2019 F350 6.7L DRW CC LB 4x4 Lariat
B&W Companion 20K for OEM pucks.
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06-12-2018, 01:26 PM
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#32
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Navy06RET
Join Date: Jun 2017
Location: St. Louis
Posts: 30
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Quote:
Originally Posted by mjones12
Who cares?
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Exactly
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06-12-2018, 03:25 PM
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#33
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Senior Member
Join Date: Jul 2015
Posts: 7,053
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Quote:
Originally Posted by dascribner
Exactly
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It appears that it is people who contribute to this forum quite a bit more than you do who care.
Bruce
__________________
2016 Rockwood Windjammer 3029W Diamond Edition
2015 Chevy 3500HD LTZ 6.0 Crew Cab 4x4 Long Bed 4.10:1 SRW
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06-12-2018, 05:40 PM
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#34
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Senior Member
Join Date: Jul 2017
Posts: 4,056
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Quote:
Originally Posted by nomad297
What kind of plumber are you? To most plumbers a PRV is a Pressure Regulating Valve, more commonly referred to as a Pressure Reducing Valve. If you are referring to a Temperature and Pressure Relief Valve, most plumbers refer to them simply as a T&P. And I don’t know any plumbers who refer to a water heater as a H/W/H — a Hot Water Heater? No. We just refer to them as Water Heaters.
Again, what are your credentials?
Bruce
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well excuse the heck out of me . brain fart on the PRV it's been awhile . now i have no need to prove didely to you . the 150psi statement is BS in the worst way . now just because you don't understand the H/W/H which if you did not know is an abbreviation. It stands for hot water heater . with out having to spell it out . kind of like using TV or TW . but i gue3ss you got it . now back to the BS 150psi lets have some facts to back that up . show me a broken psi gauge hooked up to your unit cause that's the only way you'll get a reading like that .
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06-13-2018, 07:26 AM
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#35
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Site Team
Join Date: Nov 2010
Location: Northeast Louisiana
Posts: 33,924
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OK, the site team has permanently closed this thread, as it violates several guidelines that we do enforce, which include name calling and playing nice/courteous. Also there are several members "not letting go" and even baiting.
http://www.forestriverforums.com/for...ork&page=rules
We will most likely have to delete these guideline violation posts as we discuss it.
__________________
2011 Flagstaff 831 RLBSS
A 72 hour hold in a psych unit is beginning to intrigue me as a potential vacation opportunity.
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