CTI 75mm O-ring

When I opened the plastic package of the last grain in a CTI M1590 motor, I discovered that I had a servered o-ring. This is the o-ring that is used as a spacer between grains. I need to find a replacement; Is this a common diam o-ring that I might find down at Home Depot?

Because it's only a spacer you may be able to just glue it together. Check with CTI customer service or your dealer.

It's just a spacer. Don't even have to glue it. Or use any comparable ring. Could even leave it out. Every load I have used had an extra. None needed between top grain and bulkhead or at nozzle.

Super glue works great on o rings, On very large mining equipment it's common practice to make custom/bulk type o rings and glue them together with super glue.
Kevin

jimzcatz said:

It's just a spacer. Don't even have to glue it. Or use any comparable ring. Could even leave it out. Every load I have used had an extra. None needed between top grain and bulkhead or at nozzle.

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Thought about omitting it from the top grain, just under the "washer", but the destructions said to omit it only if there wasn't room for it. ... and that's why I inquired. Thanks for the response.

It serves no purpose under the washer that I can see.

jimzcatz said:

It serves no purpose under the washer that I can see.

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What's the purpose for having them in between the grains? The only reason I can think of is for variances in grain length????

Walldiver7 said:

What's the purpose for having them in between the grains? The only reason I can think of is for variances in grain length????

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It makes for a smoother startup and burn.

markkoelsch said:

It makes for a smoother startup and burn.

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Thanks... I get an education every time I post something on TRF!

it ensures that the grains burn from the middle and the ends together, and not act as a monolithic grain (think long burn)

cbrarick said:

it ensures that the grains burn from the middle and the ends together, and not act as a monolithic grain (think long burn)

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Hypothetically speaking, If one were to leave out all of the o-rings and fashion some type of spacer on the top grain (under the washer), to assure that the grains would not "float" inside the liner,.. would the motor produce less pressure and burn longer?

maybe, if it were really tight. You'd turn it into an ex motor, though.....

Walldiver7 said:

Hypothetically speaking, If one were to leave out all of the o-rings and fashion some type of spacer on the top grain (under the washer), to assure that the grains would not "float" inside the liner,.. would the motor produce less pressure and burn longer?

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No. Floating grains are very common. The orings are there to allow a bit of space for flame travel on ignition. It would not be an ex motor.

jimzcatz said:

No. Floating grains are very common. The orings are there to allow a bit of space for flame travel on ignition. It would not be an ex motor.

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Ok... interesting. Well, it sounds like I can leave out the top o-ring with absolutely no consequences. Thanks, good to know.

The smaller Aerotech motors I fly have no rings and let the grains float.

Smaller Cesaroni motors shape the grains on one face, as if there was a tiny O ring made of propellant.

Put an Aerotech 29 or 38mm motor together WITHOUT floating grains... I dare ya!!

Walldiver7 said:

Hypothetically speaking, If one were to leave out all of the o-rings and fashion some type of spacer on the top grain (under the washer), to assure that the grains would not "float" inside the liner,.. would the motor produce less pressure and burn longer?

Click to expand...

Hypothetically speaking, if you stack the grains so tight that no cracks remain between the grains, you've converted it into a long monolithic grain. This will change the thrust curve. Instead of a mostly constant thrust, the thrust will start low and increase from then on (progressive thrust curve). Depending on some factors, this may lead to problems at startup (unstable burn) and/or at burn out (too high pressures -> cato).

Reinhard