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Old 12-30-2012, 12:55 PM   #1
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Default Gas Springs

I am installing the accy/cargo doors on my toter and need to install some gas springs to assist in opening and holding the doors open. Is there some formula to determine what size springs are required? As an example,my generator door is 54" wide,26" tall and weighs 34 lbs. The door will swing approx. 140 degree's. Each door will have two gas springs. Any input would be appreciated. I don't want to reinvent the wheel and experimenting can get expensive. MMM
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Old 12-31-2012, 08:51 AM   #2
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Good question. I bet Henry Szmyt would be a good person to ask. Find him over on the HDT forum at Escapees. Here's a thread he's been active in lately: "Sonshine Express" Wonderbed - Escapees Discussion Forum - Page 11

He's hjsdds there.
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Old 12-31-2012, 10:26 AM   #3
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Default Gas Springs

Thanks Bob,hadn't thought of that. I have been a lurker on that site for quite some time. Lot of creative folks on that site. Hope to make the Rally in Hutch next year if I can get this thing finished. Tryed to post some pictures but had some kind of problem. Computers are not my specialty... Thanks MMM
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Old 01-01-2013, 10:30 PM   #4
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Look at McMaster-Carr for gas springs..They also have a page that hgelps you choose them..I just ordered two for my murphy bed to stay up so i can use the toilet under it in my sleeper.
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Old 01-02-2013, 03:45 PM   #5
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My RV uses a spring cylinder on the interior cabinet doors to hold them up. This device has a standard coil spring inside of a tube. These springs look and work very much like the gas spring cylinders. I like the real springs because the gas/oil will never leak out and cause them to fail. The gas cylinders seem to fail at the worst times. They also don't hold the load as well in cold weather. I wonder if they are made on the larger sizes needed for you bay doors? It looks like the door on your generator compartment will be under a slide out. You might want to consider converting it to cafe' doors so that it will still open with the slide out extended.
Maybe this link will work to show what I talking about.
http://www.factoryrvsurplus.com/prod...product_id=328
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Old 01-02-2013, 06:49 PM   #6
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I recently built a project requiring I lift a 100lb door 90 degrees, but I wanted it to stay open at the top, stay closed at the bottom, and hold position through most of the in between. I took some measurements, did the math, and got reasonably close, but the truth is I had to move the mounting points around a bit before I entirely got what I wanted.

As long as the strut is strong enough, you can move the mount points around to reduce the lift force to what you want, within reason. You just end up using less of the total stroke. In general you want the longest stroke and the lowest pressure possible, otherwise you will end up putting a lot of strain on the hinges. Also you can snap the door up too fast, and the momentum of the door at the top of the travel can damage the gas spring.

If it helps, I found a calculator here, but I can't vouch for it because it is not the calculation technique that I used.

http://www.enidine.com/pdffiles/Gas_Springs.pdf

They also make gas springs that are adjustable, and by that I mean that you can reduce the pressure from factory origional, but you cannot pump it back up, so you need to be careful and bring the pressure down in small increments. That won't fix poor geometry though. You can still end up with a door that won't hold open and won't stay closed if you get the geometry wrong.

I bought mine through Maxum Hardware and the adjustable force ones are not cheap.

Ameritool Adjustable Gas Springs - Maxum Hardware

This is the web page for the one I used:

Replacement Gas Springs Per Pair - Maxum Hardware

In particular, I used the GS26-8NN-150 at 150 lbs each and $29.95 a pair. You will probably need something closer to 55 lbs if you use 2 per door, or 100 lbs if only one per door. That assumes an effective stroke of 8 to 10.78 inches, but of course you don't have to use (don't want to use) the entire stroke that is available.

If you use only one spring per door then the door needs to be strong enough in torsion to take it, and the hinges need to be strong enough to not bend, especially when pushing the door closed. I prefer a 2 spring design for anything big and heavy.

If you want to get a feel for things without doing all the heavy math then find a spring scale (fish scale) and pull the door open from your hypothetical mount point. Just be sure to pull in the same direction that the gas spring will be pushing, which implies you know the hypothetical mout point for the gas spring on the other end. Be warned though, the forces, even in your application, will be quite high.

One other warning... Since the forces are quite high, make sure the mounting balls are bolted into some solid structure, like 1/8" thick steel, otherwise they will flex and put a side load on the gas strut leading to premature failure.

Good Luck
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Old 01-03-2013, 08:52 AM   #7
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Thanks everyone for your input. I found a site that has a calculator to determine the required spring. ( I think) The site is Bansbach Easylift. The only problem I had was the dimensions are in mm and the weights are in Newtons. ( Fig Newtons are the only Newtons I was aware of) After converting all of that the calculator said I needed two 31.7 lb springs for the generator door. I found springs at pplmotorhome.com for what seems to be a reasonable price at $15 each. My choices were either 30lb or 40 lb. I elected to go with the 40 lb springs. At least this will be a starting point and I can adjust the spring size according to how they perform without breaking the bank.
Ran D., I did not try the calculator you found although it sure looks easier to use than the one I found. Also, the spring mounts will be to 14ga square tubing. Again, thanks all for the input.
Michael
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Old 01-05-2013, 09:32 PM   #8
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Your truck is looking great. One thing I just thought about. I think you aren't supposed to have the generator exhaust under the slide out. Seems to me I read that somewhere in the RVIA rules or something. My generator is mounted under my living room slide but they ran a exhaust pipe back far enough and it exits rearward of the back edge of my slide. Maybe you are doing that with your truck, I can't tell from the pictures. Sorry about the hijack of the thread too, I didn't really want to start a new topic tho.
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Old 01-06-2013, 09:25 AM   #9
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Thanks Bob. I picked up a 10 ft piece of exhaust tubing last week to do that very thing. I wasn't aware of the rules. It just makes good sense though. I plan on running it out in front of the left rear tire. I also plan on installing a smoke / carbon monoxide detector as well. Thats the great thing about this site. Lots of talented people watching and making good suggestions. Makes for a better end result. MMM
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Old 01-06-2013, 07:58 PM   #10
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Thinking out loud..and continuing the hijack of the thread...Maybe some way to run your generator exhaust into one of your exhaust stacks could be kind of cool. Would get the exhaust up and out of the imediate camp area, especially if camped right next to some one. would not think it would be too hard to find a way to tap into the elbow under the cab. Only bad thing i can think of is if there was any possiblility of exhaust gasses running back into the main engine through open valves? maybe a diverter or even running a small diameter exhaust pipe up the inside of the stack? Been thinking about this during the design of my future build. I hate it when the rig next to me is pushing their generator exhaust right into my camp site.

Dave
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