Anybody have pressure limits data for the o ring system?

[Nick B]

Using the cable tie/tube system?

What's the upper limit for commercial/local hardware o-ring design?


What industry standard o-ring number are you using for pressures beyond 300?

[air.command]

Using the cable tie/tube system?
What's the upper limit for commercial/local hardware o-ring design?
What industry standard o-ring number are you using for pressures beyond 300?

Hi Nick, what is important with o-rings is correct groove shape and gap design. The tighter the tolerance in the gap the higher the pressures you can use. For higher pressures you tend to need harder compounds also. Here is a good reference that covers o-rings in detail: http://www.parker.com/literature/ORD%20 ... ndbook.pdf

[U.S. Water Rockets1]

Using the cable tie/tube system?

What's the upper limit for commercial/local hardware o-ring design?


What industry standard o-ring number are you using for pressures beyond 300?

The size of the o-ring depends on the diameter of the opening you are trying to seal. A 0.3" opening will use a totally different size than a 3.0" opening.

[Nick B]

Using the cable tie/tube system?
What's the upper limit for commercial/local hardware o-ring design?
What industry standard o-ring number are you using for pressures beyond 300?

Hi Nick, what is important with o-rings is correct groove shape and gap design. The tighter the tolerance in the gap the higher the pressures you can use. For higher pressures you tend to need harder compounds also. Here is a good reference that covers o-rings in detail: http://www.parker.com/literature/ORD%20 ... ndbook.pdf

Thanks for the heads up. I even have some catalogs in this industry at work and home and never thought of it.

The problem to my question remains though. How this translates in our application with our random o-rings and varying interference fits. What are we seeing in real world application, what part numbers, sourced where, and limits with our designs. I can pull design pressure limits for any part number, but that will not tell me pressure failure numbers with our application.

What are your interference tolerances, your groove depth tolerances, o-ring number, and pressure failure numbers, per se....

Assuming you know them, remember them, or track them, document them.

[Nick B]

Using the cable tie/tube system?

What's the upper limit for commercial/local hardware o-ring design?


What industry standard o-ring number are you using for pressures beyond 300?

The size of the o-ring depends on the diameter of the opening you are trying to seal. A 0.3" opening will use a totally different size than a 3.0" opening.

Yes, but that's just academic.

Can you disclose numbers?

[air.command]

Thanks for the heads up. I even have some catalogs in this industry at work and home and never thought of it.

The problem to my question remains though. How this translates in our application with our random o-rings and varying interference fits. What are we seeing in real world application, what part numbers, sourced where, and limits with our designs. I can pull design pressure limits for any part number, but that will not tell me pressure failure numbers with our application.

What are your interference tolerances, your groove depth tolerances, o-ring number, and pressure failure numbers, per se....

Assuming you know them, remember them, or track them, document them.

Happy to provide any specific data on the o-rings we use. It very much depends on the application. Since most of our launchers use Gardena connectors we just use the o-rings that come with them. Only twice have we seen the o-ring on the nozzle get blown out of the groove and onto the nozzle during launch. The only other time we had o-ring failures was on the tornado tubes we machine ourselves. We use BS119 o-rings and unfortunately on a couple of the tornado tubes we didn't quite machine the o-ring seat properly and was a just little too big. The o-ring ended up blowing out on one side. So we replaced the o-ring with a harder one (90 Shore A) of the same size and the problem went away. We just use the harder o-rings on all those tornado tubes to make sure, and haven't had a problem since (even up to 250psi). All other o-rings we use including for the high pressure components are the standard 70 Shore A hardness. Other than those two incidents I don't recall having any other failures other than the normal pinched o-ring during assembly or dirt on the sealing surfaces.

All hoses we use for the launchers are scuba tank hoses so we use the standard o-rings that come with those already. Any hose connection adapters we make get made to the same spec as the hose. We use a special drill bit that drills the hole and o-ring seat of the correct shape in the one go. We then cut a thread into hole with a standard tap for the hose.

The other places we use o-rings are on the cluster and high pressure launchers or rockets. These sizes are not necessarily common because they don't fit common components used by water rocketeers. For these applications we first choose the most appropriatly sized o-ring and then look up the tables for the groove dimensions and make it to those specifications. The high pressure components we usually try to make within 0.05mm. We don't go to those tolerances for most low pressure components.

Other than o-rings we also use a lot of flat rubber washers for nozzles, Robinson couplings, commercial tornado tubes and other fittings. We first machine specifically sized brass cutters for these and then cut them out of flat rubber sheets on the drill press. (not running) We have at least 10 of these cutters now.

If you are after specific details on any of our o-ring or washer applications then I can get you those details on dimensions or materials.

[Nick B]

Thanks for the heads up. I even have some catalogs in this industry at work and home and never thought of it.

The problem to my question remains though. How this translates in our application with our random o-rings and varying interference fits. What are we seeing in real world application, what part numbers, sourced where, and limits with our designs. I can pull design pressure limits for any part number, but that will not tell me pressure failure numbers with our application.

What are your interference tolerances, your groove depth tolerances, o-ring number, and pressure failure numbers, per se....

Assuming you know them, remember them, or track them, document them.

Happy to provide any specific data on the o-rings we use. It very much depends on the application. Since most of our launchers use Gardena connectors we just use the o-rings that come with them. Only twice have we seen the o-ring on the nozzle get blown out of the groove and onto the nozzle during launch. The only other time we had o-ring failures was on the tornado tubes we machine ourselves. We use BS119 o-rings and unfortunately on a couple of the tornado tubes we didn't quite machine the o-ring seat properly and was a just little too big. The o-ring ended up blowing out on one side. So we replaced the o-ring with a harder one (90 Shore A) of the same size and the problem went away. We just use the harder o-rings on all those tornado tubes to make sure, and haven't had a problem since (even up to 250psi). All other o-rings we use including for the high pressure components are the standard 70 Shore A hardness. Other than those two incidents I don't recall having any other failures other than the normal pinched o-ring during assembly or dirt on the sealing surfaces.

All hoses we use for the launchers are scuba tank hoses so we use the standard o-rings that come with those already. Any hose connection adapters we make get made to the same spec as the hose. We use a special drill bit that drills the hole and o-ring seat of the correct shape in the one go. We then cut a thread into hole with a standard tap for the hose.

The other places we use o-rings are on the cluster and high pressure launchers or rockets. These sizes are not necessarily common because they don't fit common components used by water rocketeers. For these applications we first choose the most appropriatly sized o-ring and then look up the tables for the groove dimensions and make it to those specifications. The high pressure components we usually try to make within 0.05mm. We don't go to those tolerances for most low pressure components.

Other than o-rings we also use a lot of flat rubber washers for nozzles, Robinson couplings, commercial tornado tubes and other fittings. We first machine specifically sized brass cutters for these and then cut them out of flat rubber sheets on the drill press. (not running) We have at least 10 of these cutters now.

If you are after specific details on any of our o-ring or washer applications then I can get you those details on dimensions or materials.

I was really looking for numbers for the launch tube application, but thanks for the heads up on your applications.

[Nick B]

Using the cable tie/tube system?

What's the upper limit for commercial/local hardware o-ring design?


What industry standard o-ring number are you using for pressures beyond 300?

bump...



anybody?


uswr?

[Azriel]

What, exactly, are you looking for?

http://www.logwell.com/tech/O-ring/Parker_Handbook.pdf

Page 52 of the handbook has a small chart showing you what you can expect in terms of extrusion based failure for O-rings based on hardness of the material, pressure, and clearance of the tubes being sealed. If you can get a tight clearance (less than a .01 inch diametral difference) you can use just about any O-ring of harness 70+ up to nearly 1000PSI

[U.S. Water Rockets1]

What, exactly, are you looking for?

http://www.logwell.com/tech/O-ring/Parker_Handbook.pdf

Page 52 of the handbook has a small chart showing you what you can expect in terms of extrusion based failure for O-rings based on hardness of the material, pressure, and clearance of the tubes being sealed. If you can get a tight clearance (less than a .01 inch diametral difference) you can use just about any O-ring of harness 70+ up to nearly 1000PSI

That's the confusing part of his question. At pressures below 300PSI just about any o-ring remotely close to the bottle mouth size will work perfectly fine. Anything above 300PSI and the rocket is not going to be using random bits of bottle and pipe for the nozzle. Anyone building a high pressure rocket will likely be making custom nozzles and launchers. In such a case, the technique would be to pick a nozzle diameter that will fit the recommended size of a standard o-ring.

[Azriel]

It seems to me that for high pressures (400+psi) a flat rubber/polymer washer would be a good choice in conjunction with a flattened "plateau" on the launch tube with a recess in it to house the washer. That in conjunction with a mechanically fastening cable-tie like assembly seems to me to be a fairly ideal type of seal for extremely high pressures. Having not achieved above 250 psi in a successful launch, I'm not sure exactly what my assembly is capable of holding a seal for yet. Just out of curiosity, uswr, do you guys use some specially designed seal for higher pressures or do you use something more simple? I know a well designed O-ring assembly can easily be used in pressures in excess of 2000PSI just from looking at pressure washer hook-ups, but a water rocket is a somewhat different beast