Will o-rings be OK on HP reloads that are loaded and stored for months prior to launch?

[DavieRockets]

Due to Covid-19 I have been unable to launch using a CTI L645 that I loaded into its 75mm motor casing many months ago. I'm wondering if the forward and rear closure o-rings will "relax" and take a "set" thereby offering considerably less sealing properties. O rings were greased with synthetic grease. Usually I launch within hours of loading up.

 

[dr wogz]

Hey there Mr. Lang.. (c'est paul, ton voisin a pointe claire!)

Howe about a message to CTI? to either inquire about their opinion as to the condition after a long wait under pressure, or if they can send you a replacement set..

O-rings are pretty standard, size-wise. if you are worried, and have a set of reload instructions handy, you may be able to get a replacement set from McMaster Carr. (or a set for 10 replacements!) Swap them out before our next launch.. (Which will likely be next year [spring / summer] sometime!)

 

[Cameron Anderson]

10 years...loaded a motor in 2008, threw it in a range box and forgot about it and flew it 10 years later with zero issues.

One month is nothing. You're fine.

 

[DavieRockets]

10 years...loaded a motor in 2008, threw it in a range box and forgot about it and flew it 10 years later with zero issues.

One month is nothing. You're fine.

Thanks for that. Actually it will be more like 6 months.

 

[DavieRockets]

Hey there Mr. Lang.. (c'est paul, ton voisin a pointe claire!)

Howe about a message to CTI? to either inquire about their opinion as to the condition after a long wait under pressure, or if they can send you a replacement set..

O-rings are pretty standard, size-wise. if you are worried, and have a set of reload instructions handy, you may be able to get a replacement set from McMaster Carr. (or a set for 10 replacements!) Swap them out before our next launch.. (Which will likely be next year [spring / summer] sometime!)

Hi Paul,

I think I'll be OK with this. But Yes, I'll shoot a message off to CTI.

In the meantime, our 5 year old grandson turned up today with a birthday card for me. Since he built and launched his first rocket last month he has become rocket crazy like me!

 

[OverTheTop]

I had a K550 loaded for around 4-5 years before flight. The closures had been backed off a little prior to storage, then nipped up for flight. No problems. Was a little more difficult to light due to the grain having some surface oxidisation.

I would have no hesitation in flying the motor.

 

[o1d_dude]

I have launched motors that were two and three years old.

All I did was check the tightness of the closures, added the deployment charges and flew them like they were stolen.

I still have a few more assembled motors that have not yet flown.

 

[John Kemker]

Think about this:

Single-use motors sit for even longer periods of time without their o-rings becoming problems. You'll be fine.

 

[Steve Shannon]

Once a seal is established on an o-ring, there’s no reason it should ever unseal, unless you unseal it! You don’t loosen the parts of your car to protect the o-rings, do you?
I think the superstition around o-rings started because once upon a time some o-rings were made of a rubber that was incompatible with oil or grease. They would literally break down. The o-rings in rocket motors are not that material.

 

[prfesser]

I had a K550 loaded for around 4-5 years before flight. The closures had been backed off a little prior to storage, then nipped up for flight. No problems. Was a little more difficult to light due to the grain having some surface oxidisation.

I would have no hesitation in flying the motor.

Good point. Surface oxidation or absorption of moisture is more of an issue than o-rings. If a motor has been sitting in a tool box or similar for a long time, a somewhat more energetic starter might be a good idea. In the future, storage in some sort of airtight container is a good idea.

Best -- Terry

 

[Handeman]

Good point. Surface oxidation or absorption of moisture is more of an issue than o-rings. If a motor has been sitting in a tool box or similar for a long time, a somewhat more energetic starter might be a good idea. In the future, storage in some sort of airtight container is a good idea.

Best -- Terry

Totally agree!

I drop a small descant in a baggie/plastic bag and tape it tight around the nozzle end. A scrap of paper in there with the motor info doesn't hurt either if it's going to be a long time in storage.

BTW, blue painters tape seems to come off cleaner/better after a long time than other types of tape.

 

[OverTheTop]

Good point. Surface oxidation or absorption of moisture is more of an issue than o-rings. If a motor has been sitting in a tool box or similar for a long time, a somewhat more energetic starter might be a good idea. In the future, storage in some sort of airtight container is a good idea.

I now wrap the motors in food wrap for storage, and use a bit of white lightning grain to augment the igniter.

 

[OverTheTop]

A scrap of paper in there with the motor info doesn't hurt either if it's going to be a long time in storage.

I write it on with a sharpie before the wrap.

 

[ericm541]

I've had motors built for extended period of time, it should be fine just store it appropriately, you can always take off the aft ring and check.

 

[cbrarick]

i just tape over the nozzle, and use a sharpie to write down the load. on the tape. I had a cti 75 mm M loaded for almost 4 years, no problems.

 

[AeroTech]

The concern came about with the older high power RMS reloads that used O-rings that sealed against the forward end of the delay element. The thought was that the delay propellant could acquire a compression set over time and the O-ring would not provide an effective seal. After the “RMS-Plus” design was introduced with the circumferential seal around the plastic delay tube, that issue was eliminated. However, the model rocket-size reloads (18/20, 24/40 etc.) still use the face seal on the delay.

Once a seal is established on an o-ring, there’s no reason it should ever unseal, unless you unseal it! You don’t loosen the parts of your car to protect the o-rings, do you?
I think the superstition around o-rings started because once upon a time some o-rings were made of a rubber that was incompatible with oil or grease. They would literally break down. The o-rings in rocket motors are not that material.

 

[Jay Rairigh]

However, the model rocket-size reloads (18/20, 24/40 etc.) still use the face seal on the delay.

So...could it be an issue on these model size reloads using the face seal?

 

[Steve Shannon]

The concern came about with the older high power RMS reloads that used O-rings that sealed against the forward end of the delay element. The thought was that the delay propellant could acquire a compression set over time and the O-ring would not provide an effective seal. After the “RMS-Plus” design was introduced with the circumferential seal around the plastic delay tube, that issue was eliminated. However, the model rocket-size reloads (18/20, 24/40 etc.) still use the face seal on the delay.

That’s understandable. Thanks for educating me. Did you ever experience that?

 

[John Kemker]

So...could it be an issue on these model size reloads using the face seal?

very doubtful

 

[Ez2cDave]

10 years...loaded a motor in 2008, threw it in a range box and forgot about it and flew it 10 years later with zero issues.

How did you remember which reload was in the case ?

Dave F.

 

[Cameron Anderson]

How did you remember which reload was in the case ?

Dave F.

Masking tape and sharpie. I always load my motors at home in my garage with good light, no wind, and no dirt. Then I throw a piece of tape on the case and write the load date and reload on the tape.
Usually I fly my motors within a week or two, sometimes it'll be a year.

 

[rocketman4h]

Don't you all forget the 75mm casing o-rin with greased prior to installiation. This grease will greatly help in repelling oxidation. water and other contaminants from degrading the o-ring.I have been a fluid power specialist for more than 30 years and have seen o-rings on systems that run on 5000 psi last for 20 years! Your engine should be fine.

 

[dr wogz]

I usually wrap the motor face-card around the rocket (and held with an elastic) to know what I have loaded in what rocket when I build mine away from the field (even on the field sometimes!) I'll also scratch on the delay time with a pen..

One habit I hope to star next yer, it to write the motor used & date on a fin after each flight. That way, I now how many times I've flow it, and with what motor (instead of having to record this all on a separate sheet & such). It'll also be a bit of a 'bragging rights' as i walk around with it, at the RSO table, on the pad, etc..

 

[Binder Design]

It will actually seal better as long as the o-rings were lubed. O-rings absorb the lubricant and swell, making the seal tighter.