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Old 10-22-2014, 07:36 AM   #15
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I sneezed inside with all the windows and doors closed. Over $10k in damages once I replaced all the windows, vents, and the windshield. I'm just glad I wasn't driving at the time.
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Old 10-22-2014, 07:39 AM   #16
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When I saw the headline I thought maybe you'd eaten too many burritos....
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Old 10-22-2014, 07:44 AM   #17
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While I would agree that the tech overstated the need to provide some sort of ventilation while moving the slides, I was given similar advice by a very experienced tech during the PDI on my current coach. His recommendation was to open the small toll window when operating the slides. This was primarily due to having one Power Gear slide (to minimize stress on the mechanism). In fact, when I move those slides out, there is the equivalent of a small hurricane coming in that window due to air movement. So, if a coach is tight, well sealed, I can see opening a window or the door can be helpful.
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Old 10-22-2014, 02:01 PM   #18
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Now, wait a minute.....

Last night about midnight I read this thread, and responded with "utter tripe".

A bit later, as I was falling asleep, a little voice in my head kept whispering "What would Boyle say?" This morning the voice was still there, so after breakfast I started digging. Bottom line is that the tech has a point. Not a strong point, mind you, -in fact a rather weak one- and surrounded by a load of assumptions, caveats and provisos, but a point nonetheless.

Here's the nut, simply put. >>and for those of you who spent undergrad nights in an Irish Pub talking with Boyle, cut me some slack here. I'm dredging up stuff I paid very little attention to 50 years ago.<<

Air, for the most part, behaves in a linear way. If you have a certain amount of air in a container and you then squeeze the container down to reduce the volume, the air pressure on the inside of the container will increase proportionally. Volume down--pressure up. Volume up-pressure down. Simple. Cut the volume in half and the pressure doubles. Expand to double the volume and the pressure reduces by half. Easy beans.

My 40 ft Dutch has about 2200 cu ft of volume, give or take. If the kitchen and bedroom slides are already in they're not a factor. But if the living room slide is still out, that's another 220 cu ft +/-. So when I retract the LR slide I'm squeezing an additional 220 cf of air into a space that can only hold 2200 cf. I'm reducing the volume by 10%, so according to this guy Boyle the pressure inside the coach has to go up by 10%.

Up to what? From what? Outside air pressure is usually around 15.7 psi. It varies around a little with the weather, but 15.7 is a good number. Now if everything's normal the air pressure inside the coach will be exactly the same as outside, otherwise the walls would blow out, or collapse inward. But as we bring in the slide, and reduce the available volume for all that air by 10%, then the pressure inside has to go up by 10%. 10% of 15.7 psi is 1.57 psi (call it 1.6) so the pressure inside the coach will climb to 17.3 psi. 15.7psi outside the coach, 17.3psi inside. That extra 1.6psi is pushing outward all over the coach.

The windshield on my Dutch has about 5200 sq inches, give or take. 1.6 psi over 5200 sq inches equals-- 8320 lbs of force pushing the windshield out of the coach! Over 4 tons of pressure! Sounds pretty convincing, doesn't it? 1.6psi sounds like it can be a lot of pressure. Just by way of comparison, when you're flying high in an airliner the pressure differential (dp) between the inside of the plane and the outside usually runs on the order of 8psi.

Remember what I said before about "...Not a strong point, mind you, and surrounded by a load of assumptions, caveats and provisos..."? Well, the two biggest assumptions are 1) that the entire coach structure is absolutely, positively airtight through the whole procedure, and 2) the windshield mounting seal is the weakest structural point in the entire coach. If both of these were true, then the windshield might pop loose from its seal, but I don't think it would explode outward.

But in fact, neither of these is true, so I will downgrade my previous comment from "utter tripe" to the more simple "tripe".
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Old 10-22-2014, 02:07 PM   #19
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So far the responses are much more reserved and polite than that I gave my friends. I'd repeat it but the moderators would kick me off.

What's sad is our friends are trusting and believed the guy. Makes you wonder how many other newbies have been mislead by total nonsense.

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yes i can feel you there on the admin

many times i have seen a over use of power when there really is no need for it

even some thing small like this i am sure would be ..... hey where did i go
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Old 10-22-2014, 02:23 PM   #20
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Quote:
Originally Posted by JFXG View Post
Last night about midnight I read this thread, and responded with "utter tripe".

A bit later, as I was falling asleep, a little voice in my head kept whispering "What would Boyle say?" This morning the voice was still there, so after breakfast I started digging. Bottom line is that the tech has a point. Not a strong point, mind you, -in fact a rather weak one- and surrounded by a load of assumptions, caveats and provisos, but a point nonetheless.

Here's the nut, simply put. >>and for those of you who spent undergrad nights in an Irish Pub talking with Boyle, cut me some slack here. I'm dredging up stuff I paid very little attention to 50 years ago.<<

Air, for the most part, behaves in a linear way. If you have a certain amount of air in a container and you then squeeze the container down to reduce the volume, the air pressure on the inside of the container will increase proportionally. Volume down--pressure up. Volume up-pressure down. Simple. Cut the volume in half and the pressure doubles. Expand to double the volume and the pressure reduces by half. Easy beans.

My 40 ft Dutch has about 2200 cu ft of volume, give or take. If the kitchen and bedroom slides are already in they're not a factor. But if the living room slide is still out, that's another 220 cu ft +/-. So when I retract the LR slide I'm squeezing an additional 220 cf of air into a space that can only hold 2200 cf. I'm reducing the volume by 10%, so according to this guy Boyle the pressure inside the coach has to go up by 10%.

Up to what? From what? Outside air pressure is usually around 15.7 psi. It varies around a little with the weather, but 15.7 is a good number. Now if everything's normal the air pressure inside the coach will be exactly the same as outside, otherwise the walls would blow out, or collapse inward. But as we bring in the slide, and reduce the available volume for all that air by 10%, then the pressure inside has to go up by 10%. 10% of 15.7 psi is 1.57 psi (call it 1.6) so the pressure inside the coach will climb to 17.3 psi. 15.7psi outside the coach, 17.3psi inside. That extra 1.6psi is pushing outward all over the coach.

The windshield on my Dutch has about 5200 sq inches, give or take. 1.6 psi over 5200 sq inches equals-- 8320 lbs of force pushing the windshield out of the coach! Over 4 tons of pressure! Sounds pretty convincing, doesn't it? 1.6psi sounds like it can be a lot of pressure. Just by way of comparison, when you're flying high in an airliner the pressure differential (dp) between the inside of the plane and the outside usually runs on the order of 8psi.

Remember what I said before about "...Not a strong point, mind you, and surrounded by a load of assumptions, caveats and provisos..."? Well, the two biggest assumptions are 1) that the entire coach structure is absolutely, positively airtight through the whole procedure, and 2) the windshield mounting seal is the weakest structural point in the entire coach. If both of these were true, then the windshield might pop loose from its seal, but I don't think it would explode outward.

But in fact, neither of these is true, so I will downgrade my previous comment from "utter tripe" to the more simple "tripe".
Wow, that was an impressive post! How did you sleep with all of that on your mind? I got a headache just trying to keep up with it. I am simply going to keep one of the four roof vents with maxxair screened covers on them on our coach open just in case. . .
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Old 10-22-2014, 06:55 PM   #21
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Actually that is a very popular myth and more than one tech (or sales guy) has given that advice, usually in very hushed and sincere tones. I wish my coach, and especially the slide seals, was anywhere near tight enough to do something like that.

I've seen the air movement blow a curtain or blind up against a window screen, though. Theer is a lot of air volume in play, even if the pressures never gets real high.
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Old 10-22-2014, 06:56 PM   #22
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Never heard of a windshield blowing out but years ago have heard of people being bothered by the fast movement of their slide that would cause air pressure causing their eye drums to pop.
They resolved it by opening a window.
The slides were hydraulic type operation and fast.
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Old 10-22-2014, 08:28 PM   #23
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Do you really get up in the morning and go thru calculations like that? Reminds me of that cartoon character I watched as a kid...Tom Terrific. He would put on his thinking cap and when he came up with the solution, a light bulb would appear and he would exclaim "Eureka...I've got it!"

PS - I have also heard of this type of behavior referred to as "mental masturbation." Oh well....
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Old 10-22-2014, 10:07 PM   #24
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Blowing Out The Windshield

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Originally Posted by Firebug5 View Post
Wow, that was an impressive post! How did you sleep with all of that on your mind? I got a headache just trying to keep up with it. I am simply going to keep one of the four roof vents with maxxair screened covers on them on our coach open just in case. . .
I enjoy the overthinking of others, it makes me feel better about my many times of overthinking something....

I barely thought about this thread after I read it, except to see what others may have said.... And I see that others make life interesting with the varied comments on a subject as this....

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JFXG, Do you really get up in the morning and go thru calculations like that? .... I have also heard of this [ .. ] as "mental masturbation." Oh well....

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Old 10-22-2014, 11:00 PM   #25
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JFXG
Do you really get up in the morning and go thru calculations like that? Reminds me of that cartoon character I watched as a kid...Tom Terrific. He would put on his thinking cap and when he came up with the solution, a light bulb would appear and he would exclaim "Eureka...I've got it!"

PS - I have also heard of this type of behavior referred to as "mental masturbation." Oh well....

Yes, I do, baron. It's called thinking, a process used to determine facts and accuracy prior to making a statement. It's really quite a reliable process, unlike the bitter, vituperative, and inaccurate rant of yours I just read a few moments ago in a thread about extended service contracts. Thinking. Make a note. Try it.
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Old 10-22-2014, 11:51 PM   #26
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Blowing Out The Windshield

Put 'em up, put 'em up.... Just don't blow out the windshield while the hot air escapes.... LOL


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Old 10-23-2014, 12:11 AM   #27
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No way that tech is a idiot.
This is a classic example of how punctuation can completely change the meaning of a sentence:

"No way that tech is an idiot" is a lot different than "No way - that tech is an idiot"

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...That extra 1.6psi is pushing outward all over the coach.
A fairly decent treatise on our dear friend Boyle but I have a couple of comments:

1. Here on earth the mean atmospheric pressure is 14.7 psi, not 15.7...

2. Reducing the volume in the container would cause the increase in pressure if the container was airtight. But as soon as the slide starts its inward journey you'll notice that most of them have at least an inch or more of clearance on at least the vertical edges, and the top edge as well - that's enough so that as the very slow-moving slide comes in the added pressure can easily escape around the slide opening.

The bottom line is - if your rig is air-tight enough to worry about the windshield popping out when operating the slides, then you also have to worry about the pressure increase when it's sitting in storage and the interior temperature rises as the sun beats down on it!
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Old 10-23-2014, 12:31 AM   #28
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.....

1. Here on earth the mean atmospheric pressure is 14.7 psi, not 15.7...

2. Reducing the volume in the container would cause the increase in pressure if the container was airtight....

1) Thank you. A regretted error. Ref my Para #3. Slightly alters the equation without affecting the outcome.

2) Already addressed. Ref my Paras #2, 8, 9.
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