K185/Seal Disk question

[SpartaChris]

I know Aerotech switched from using the forward insulator to the forward seal disk in the K185 motor some time back. I assembled one today in preparation for next week's RocStock using the seal disk instead of the insulator and there is now a 1/8" gap when I tighten the aft closure. I'm wondering if this is normal, or if I should omit the seal disk and use the insulator instead?

It's an older motor with directions that mention nothing about using the seal disk.

Thanks in advance.

 

[cjl]

If it still snugs down properly, and it feels like the O-rings are properly compressed, it should work fine. I'd fly it...

 

[ben_ullman]

If it still snugs down properly, and it feels like the O-rings are properly compressed, it should work fine. I'd fly it...

Yes! DO NOT Leave the new disk out or you will void warranty. If the motor CATO's then keep all the reminants and return to AT.

Ben

 

[SpartaChris]

Thanks guys for replying. I just got a response back from Gary and he said to omit the seal disk and go with the fwd. insulator. That 1/8" gap in the back makes it hard for me to believe the seal ring is actually sealing inside, so I'll just follow Gary's advice.

 

[ben_ullman]

Thanks guys for replying. I just got a response back from Gary and he said to omit the seal disk and go with the fwd. insulator. That 1/8" gap in the back makes it hard for me to believe the seal ring is actually sealing inside, so I'll just follow Gary's advice.

wow. Thats suprising. In my mind the liner was just a tad to long.

Ben

 

[SpartaChris]

wow. Thats suprising. In my mind the liner was just a tad to long.

Ben

You know, I didn't even think about that. For what it's worth, this is an older motor. The directions don't have anything about the seal disk. They just feature the insulator.

The other thing I note is when I have it all together with the seal disk, there is no back and forth slop in the propellant like you have with the insulator. So that makes me wonder- what is the difference between the newer motors that utilize the seal disk by default and the older ones that utilized the insulator disk? Is the motor and liner just a smidge shorter in the newer ones vs. older ones?

 

[GaryT]

When using the seal disc on the older load you don't use the fiber washer OR the 1/16th O-Ring that goes between the nozzle and the liner tube.

 

[SpartaChris]

When using the seal disc on the older load you don't use the fiber washer OR the 1/16th O-Ring that goes between the nozzle and the liner tube.

OH! That totally makes sense. Is that documented somewhere?

 

[GaryT]

If you go onto the AT web site you can view all there Re-Load Instructions, New and old, Thing is I didn't see any New! Instructions for the K185? every other load that fits the 54/1706 case (New Version with seal disk) Instructions omit the Fiber washer and Nozzle/Liner tube O-Ring.

 

[SpartaChris]

If you go onto the AT web site you can view all there Re-Load Instructions, New and old, Thing is I didn't see any New! Instructions for the K185? every other load that fits the 54/1706 case (New Version with seal disk) Instructions omit the Fiber washer and Nozzle/Liner tube O-Ring.

I checked the instructions first before I posted the question and didn't see any modifications showing the use of the seal disk. I also checked the instructions for the K550 posted to their website and saw they had the old way of using the fiber washer as well.

https://www.aerotech-rocketry.com/c...S_Instructions/54mm/54_852-1706w_in_20070.pdf

I did see the method you described for the K805 though.

I shot Gary another e-mail to see what he thinks. I've flown plenty of these the old sk00l way without the seal disk in the past and had no problems, so I'm not overly worried about it. I just haven't flown one since the method changed, so I want to be sure to get it right in case there is a problem.

Thanks again for all your help.

 

[GaryT]

They also list the Newer instructions using the Seal disc for the W T F R, Just not for the long Burn loads which is weird?.

 

[ben_ullman]

I think alot of the reason they changed to the aluminum disk is due to the K1275. I have flown 5 in my polecat saturn and 4 out of the 5 bubbled/burned the case. Even WITH the new design

Ben

 

[SpartaChris]

They also list the Newer instructions using the Seal disc for the W T F R, Just not for the long Burn loads which is weird?.

Well DUH, they were right in front of me the whole time.

So I tried omitting the o-ring that goes in between the nozzle and liner and omitting the insulator and there is still a decent gap almost the same size in the aft closure when I tighten it down.

Kinda odd. I also noticed the K185 isn't on the list of motors from the news release needing the seal disk anyway, and since it doesn't appear in the instructions, perhaps I'm not supposed to use it?

It's a borrowed casing and I'd really like not to void the warranty if something happens. Like I said before, I've flown this motor dozens of times the old way without issues, so I just wanna get this right.

Thanks for your patience.

 

[Rocketjunkie]

If your reload came with the phenolic washer and nozzle to liner O-ring, you have an older reload. Build it per the directions, it will work just fine.

 

[cjl]

I think alot of the reason they changed to the aluminum disk is due to the K1275. I have flown 5 in my polecat saturn and 4 out of the 5 bubbled/burned the case. Even WITH the new design

Ben

That almost sounds like you're doing something wrong. I've never flown one, but I've seen 8 or 10 flown without the slightest issue.

 

[SpartaChris]

If your reload came with the phenolic washer and nozzle to liner O-ring, you have an older reload. Build it per the directions, it will work just fine.

Oh I'm sure it will. As I said before, I've flown enough of these without the seal disk that I'm confident it will work. I just wanted to make sure I don't void the warranty if something were to happen. I double checked with Gary (again) and he said the same thing- Just use the parts that came with the kit.

Furthermore, it turns out the K185 is the one motor for that casing that doesn't require the seal disk. Everything else needs it.