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Damaged O-ring in ZWO 7x2 filter wheel

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#1 DarkSkyLover

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Posted 25 May 2023 - 10:17 PM

I just encountered a problem with my ZWO 7x2 filter wheel. The Sky X which is controling my equipement is reporting "moving" as soon as I connect the filter wheel. The wheel stays blocked between the green and the blue filters. I opened the filter wheel casing and, sure enough, there is a fairly deep dent in the orange flexible o-ring that goes around the wheel (attached photo). This dent causes the wheel to jam there when it meets the little motor axis. I don't understand why there is a dent, my equipment (Celestron Edge HD14 on a Paramount MX+) stays in the observatory and there has been no equipment drop or collision with the pier or such. 

 

I don't think I can repair the dent with any type of filler as this is flexible material. Does anyone know if I can source this O-ring other than through ZWO? I am trying to avoid the shipping delays and cost from China. If I can not find it anywhere in North America, then I will contact ZWO.

 

Thanks!

 

20230525_222640.jpg

Damaged ZWO 7x2 EFW reduced.jpg



#2 Another_Dave

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Posted 26 May 2023 - 12:02 AM

I don't know what there is a dent either. It is the sort of thing that a critter might try as taste of. But it's perhaps not a coincidence that the size and shape of the divot matches pretty well to the diameter of the drive shaft which also seems to have some orange residue on it. I wonder whether it jammed at some point and the shaft spun in place and melted the O-ring? Maybe check the system for any causes of fouling as part of the repair?

 

My guess is that it should be a Metric sized O-Ring. If you use callipers to measure the Radial Cross Section of the rubber (mm [A]) and a ruler to measure the Inside Diameter of the ring (mm [BBB]) you should get a size of AxBBB to compare with available options.

 

I believe the ring diameter is measured with the O-Ring in an un-stretched state, though I would measure it on the wheel as one point of reference, then do my best to make multiple measurements across with it off and average those to get an idea of the size un-stretched. Then look for options that will be similar. While the diameter of the rubber will be critical, the diameter of the circumference should not be as strict so long as it stretched about the right amount to be taught when fitted to the wheel.

 

These off-the-shelf O-Rings will probably be black, nitrile rubber in most cases rather than whatever ZWO used. A range of specialty hardware vendors sell O-rings online. What options are best in Canada is beyond my knowledge. In that size range you are perhaps looking at $US20 per O-Ring .. something like that.


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#3 briansalomon1

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Posted 26 May 2023 - 11:35 AM

Since that o-ring is only there to provide traction, you can use any soft o-ring material. N-buna is usually the least expensive. Silicone will perform better in very cold environments.

 

If you buy a length of O-ring cord, you can simply make an O-ring of any size you want yourself. It takes no skill or special materials. Simply remove the existing O-ring and measure the length. You can cut it at this point to make this easier.

 

Measure a section of the new O-ring material and cut to the desired length. Use a very sharp blade and slide it gently across to make a square cut.

 

Simply superglue the ends together. Sand the bond with #220 sandpaper and install.

 

I've made O-rings this way for many years and have installed them on high vacuum valves/fittings and none of these O-rings have ever failed in service.

 

https://www.ebay.com...kp:BFBMvqr8jYti


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#4 DarkSkyLover

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Posted 26 May 2023 - 01:42 PM

I don't know what there is a dent either. It is the sort of thing that a critter might try as taste of. But it's perhaps not a coincidence that the size and shape of the divot matches pretty well to the diameter of the drive shaft which also seems to have some orange residue on it. I wonder whether it jammed at some point and the shaft spun in place and melted the O-ring? Maybe check the system for any causes of fouling as part of the repair?

 

My guess is that it should be a Metric sized O-Ring. If you use callipers to measure the Radial Cross Section of the rubber (mm [A]) and a ruler to measure the Inside Diameter of the ring (mm [BBB]) you should get a size of AxBBB to compare with available options.

 

I believe the ring diameter is measured with the O-Ring in an un-stretched state, though I would measure it on the wheel as one point of reference, then do my best to make multiple measurements across with it off and average those to get an idea of the size un-stretched. Then look for options that will be similar. While the diameter of the rubber will be critical, the diameter of the circumference should not be as strict so long as it stretched about the right amount to be taught when fitted to the wheel.

 

These off-the-shelf O-Rings will probably be black, nitrile rubber in most cases rather than whatever ZWO used. A range of specialty hardware vendors sell O-rings online. What options are best in Canada is beyond my knowledge. In that size range you are perhaps looking at $US20 per O-Ring .. something like that.

I agree with your evaluation. The wheel must have been stuck and the "change filter" command must have driven the shaft through the soft material of the o-ring. I could not find any resistance anywhere while rotating the wheel manually, so I don't know what might have caused this "seizure".What I did for now is simply turned the o-ring around so that the indent is inside, resting against the wheel and leaving the outside surface smooth. However, this will certainly make it a weak area subject to break eventually. My distributor has contacted ZWO by now and is trying to get a replacement part for free smile.gif . Thanks for your response!



#5 DarkSkyLover

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Posted 26 May 2023 - 01:47 PM

Since that o-ring is only there to provide traction, you can use any soft o-ring material. N-buna is usually the least expensive. Silicone will perform better in very cold environments.

 

If you buy a length of O-ring cord, you can simply make an O-ring of any size you want yourself. It takes no skill or special materials. Simply remove the existing O-ring and measure the length. You can cut it at this point to make this easier.

 

Measure a section of the new O-ring material and cut to the desired length. Use a very sharp blade and slide it gently across to make a square cut.

 

Simply superglue the ends together. Sand the bond with #220 sandpaper and install.

 

I've made O-rings this way for many years and have installed them on high vacuum valves/fittings and none of these O-rings have ever failed in service.

 

https://www.ebay.com...kp:BFBMvqr8jYti

Thanks for the link, this is rather inexpensive. I will see if my distributor is able to get a replacement O-ring from ZWO for free. If not, I will go ahead and make one myself using the link you provided. Thank you for your help!




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