Pyrovalves / Pyrotechnic valves

[G_T]

PS - If you dig there are plenty of research papers on hybrids published. There are some books available on the subject. I recommend reading up before designing. Then you'll at least have an idea of most/all of the main issues you have to design around. So then even TLAR engineering has a better chance of working. TLAR has little chance of working if you don't know the questions beforehand.

I spent quite a while reading and studying before I started designing. Then I spent a while designing. And even so I missed one issue where TLAR bit me because I didn't run the numbers beforehand for that particular thing but instead relied on related experience which wasn't as related as I had thought. Had I run that set of numbers, I'd have known it was doomed to fail - in just the way it failed.

Gerald

 

[jjrgray]

PS - If you dig there are plenty of research papers on hybrids published. There are some books available on the subject. I recommend reading up before designing. Then you'll at least have an idea of most/all of the main issues you have to design around. So then even TLAR engineering has a better chance of working. TLAR has little chance of working if you don't know the questions beforehand.

I spent quite a while reading and studying before I started designing. Then I spent a while designing. And even so I missed one issue where TLAR bit me because I didn't run the numbers beforehand for that particular thing but instead relied on related experience which wasn't as related as I had thought. Had I run that set of numbers, I'd have known it was doomed to fail - in just the way it failed.

Gerald

Thanks Gerald you have been really helpful. In terms of back flow of nitrous, could it be stopped by using a flashback arrestor or a non-return (one way) valve in-between the oxidiser tank and the combustion chamber? Obviously I would like to avoid a big boom.

 

[AeroTech]

Hi guys,

Does anybody know anything about pyrovalves being used in hybrid engines. I have done a bit of research and I think Aerotech and Contrail use them in a few of their commercially available hybrid engines? I am designing and building a hybrid engine with a few of my mates (one of who is writing an EPQ on it) and I would very much like to use a pyrovalve instead of a solenoid valve in-between my internal engine tank and my combustion chamber so that I can ignite both the fuel grain and start the flow of oxidiser at the same time in a relatively easy way. I have so far not had any luck finding pyrovalves online for the scale I am working on (indeed for model rocketry at all), with all the hits coming up as commercial rocket pyrovalves which cost literally thousands of pounds/GBP (I live in the UK).

Any help would be much appreciated - I just want to learn.

Many thanks,
Jack

http://www.aerotech-rocketry.com/cu...tructions/RMS-Hybrid/54mm_hyb_in_man_6-98.pdf
http://www.aerotech-rocketry.com/uploads/6eeae0f9-2526-45be-86bd-d132c28d6629_pyrovalve_5579636.pdf
https://www.rocketmotorparts.com/RMSHybrid_Data_Pack/p1577809_16042498.aspx

 

[jderimig]

I have flown N2O hybrids both commercial and research for about 15 years now. Ignition with the Contrail method of U/C valve and Pyrodex pellets has been 100% successful for me. I have never had a failed ignition with that method in about 30-40 ignitions so far. You may want to consider it if you can emulate that method even though you are not using the tube for a fill. It simply works.

For avoiding blow back I would just recommend starting with injector size nozzle size ratio of the closest Contrail to your motor size. Sufficient pressure drop across the injector is all that is needed robust flash back robustness.

Research papers are nice but reverse engineering existing proven designs should be a major part of your study. Existing very reliable designs exist, please start there and be VERY wary of deviating from existing design parameter if this is your first go at hybrids. Don't reinvent the wheel and don't learn design weaknesses that have already been learned.

Here is one of my flights, instant on, U/C valve, 2 pyrodex pellets, 750psi N2O. Video show detail of motor injector ignition assembly.

https://youtu.be/nWRiRxLtGaI

 

[Ez2cDave]

You need to use grease and O-rings that are suitable for an oxidizer rich environment.

"KRYTOX" is one example.

A pic of my HYPERTEK motors, just before I sold all of them after the BATFE lawsuit victory.

CONTRAIL data below . . .

Dave F.

 

[rocket_troy]

In terms of back flow of nitrous, could it be stopped by using a flashback arrestor or a non-return (one way) valve in-between the oxidiser tank and the combustion chamber?

For smaller to mid size motors just ensure there's enough pressure drop over the injector ie. run your chamber maybe 300 psi lower than the tank pressure, utilise longer orifices with reasonable thermal conductivity and use more smaller orifices instead of 1 or a small number of larger ones.
For large motors - then look seriously at check valves.
If using check valve(s), it obviously makes filling through the injector more challenging (if using UC type arrangement) although I've developed designs to allow it, but generally you would top fill if remote filling.

TP

 

[boatgeek]

Understood. I already have a big field where we static test and I'm working on making more and more of the GSE remote so there can be a big exclusion zone in case of explosions and shrapnel. All about that safety!

FWIW, my old child's Spaceport America team tested their O-class hybrid in a decent size logging yard. Humans were on the other side of a shipping container at a decent distance and/or behind a berm during the test firing. I would be in favor of having some steel, concrete, or dirt in between you and a tank that might blow.

 

[jjrgray]

FWIW, my old child's Spaceport America team tested their O-class hybrid in a decent size logging yard. Humans were on the other side of a shipping container at a decent distance and/or behind a berm during the test firing. I would be in favor of having some steel, concrete, or dirt in between you and a tank that might blow.

We do also have a chunky berm in this field I mentioned.

 

[jjrgray]

For smaller to mid size motors just ensure there's enough pressure drop over the injector ie. run your chamber maybe 300 psi lower than the tank pressure, utilise longer orifices with reasonable thermal conductivity and use more smaller orifices instead of 1 or a small number of larger ones.
For large motors - then look seriously at check valves.
If using check valve(s), it obviously makes filling through the injector more challenging (if using UC type arrangement) although I've developed designs to allow it, but generally you would top fill if remote filling.

TP

How would you ignite the fuel grain if using a top fill method? Would you still use a preheater solid propellant like some of those found in larger UC type arrangements?

 

[rocket_troy]

How would you ignite the fuel grain if using a top fill method? Would you still use a preheater solid propellant like some of those found in larger UC type arrangements?

Well, you could pretty much (without even getting clever) use exactly the same arrangement as a typical UC, sure... That hose would just be capped/blocked at some distance from the fitting/preheating grain - likely just outside the nozzle to ensure there's no chance of metallic objects hitting/blocking the nozzle on the way out. I have flown that configuration with success, but I'm not a big fan of top filling after forgetting to disconnect fill hose at one launch where there was a myriad of unexpected distractions happening at that moment. Fortunately it wasn't even noticeable with the racket and flare

Or you could use a pyrovalve instead and have no hose within the chamber.



TP

 

[jjrgray]

Well, you could pretty much (without even getting clever) use exactly the same arrangement as a typical UC, sure... That hose would just be capped/blocked at some distance from the fitting/preheating grain - likely just outside the nozzle to ensure there's no chance of metallic objects hitting/blocking the nozzle on the way out. I have flown that configuration with success, but I'm not a big fan of top filling after forgetting to disconnect fill hose at one launch where there was a myriad of unexpected distractions happening at that moment. Fortunately it wasn't even noticeable with the racket and flare

Or you could use a pyrovalve instead and have no hose within the chamber.



TP

I think I'm going to forgo the pyrovalve idea as it will cause more issues than it solves and I am not very confident with the idea. Would it be feasible to use a (normally open) solenoid valve and energise it during the top filling to keep the nitrous out of the engine, then de-energising it in sync with an ignition charge? This idea to me has good face value but can you see any blaring issues that I've looked over?

 

[rocket_troy]

Solenoid valves - the ones rated for both N2O pressures and reasonable throughputs (which you'll need even for modest size hybrids) will tend to be quite beefy and heavy also requiring reasonable current flows... well... to at least open. What's more, it's mass and space that just doesn't need to be there. Not recommended.

Regarding Pyro valves - the people that do use them generally keep using them with good success. There's no glaring inherent flaw with the concept. Of course details matter. They do have some worthy advantages over something like U/C such as - more reluctance to hard start (I've personally never heard of it happening with a pyro valve hybrid) and they also allow for a little bit more variation with injector design.

TP

 

[jjrgray]

Solenoid valves - the ones rated for both N2O pressures and reasonable throughputs (which you'll need even for modest size hybrids) will tend to be quite beefy and heavy also requiring reasonable current flows... well... to at least open. What's more, it's mass and space that just doesn't need to be there. Not recommended.

Regarding Pyro valves - the people that do use them generally keep using them with good success. There's no glaring inherent flaw with the concept. Of course details matter. They do have some worthy advantages over something like U/C such as - more reluctance to hard start (I've personally never heard of it happening with a pyro valve hybrid) and they also allow for a little bit more variation with injector design.

TP

Okay that's quite helpful actually. RE pyro valves in a hybrid, what would the general design of one of them look like? I am cautious of straying into the research forum material... however just knowing the general design of a pyro valve would help immensely in seeing if I could work it into my current design. No specifics, just a general overview.

 

[heada]

Solenoid valves of a size and power to do fill lines typically pull a decent amount of power and get quite warm as well. Just something to factor in to your plans if you go that route.

 

[rocket_troy]

Attached gif animation (hopefully it animates)

 

[jjrgray]

Attached gif animation (hopefully it animates)

Cheers, the animation does work by the way. So I am guessing the brown is your solid charge?

 

[jjrgray]

Solenoid valves of a size and power to do fill lines typically pull a decent amount of power and get quite warm as well. Just something to factor in to your plans if you go that route.

If I did go down the solenoid valve route (using one to control to control the flow of nitrous from the internal oxidiser tank the combustion chamber) I would use an external power supply from my GSE in order to keep the valve closed during filling and venting of the internal nitrous tank. The solenoid valve would be normally open so that during the fill it would be energised and during the burn it could be deenergised to allow the flow of nitrous. The way I have drawn up the design for the solenoid valve version is using magnetic wire connectors that are sunk into the fuselage and then connected magnetically to wires from the an external GSE power supply and radio receiver. Then the idea is that an ignition charge will be triggered in the fuel grain and the solenoid valve would be deenergised allowing the flow of nitrous to the combustion chamber. Then the rocket can launch and the magnetic connection between GSE electrical wires and the wires going to the solenoid will break. To manage the heat a 'solenoid saver' would be installed together with the solenoid valve and small orifice could be made in the fuselage to direct cooling air towards the solenoid. Just one idea I had. Any thoughts?

 

[AeroTech]

Just FYI the original AeroTech hybrid motor design employed a coaxial solenoid valve, but that was quickly abandoned and replaced with the pyrovalve which was deemed much simpler and more reliable.

 

[jjrgray]

Just FYI the original AeroTech hybrid motor design employed a coaxial solenoid valve, but that was quickly abandoned and replaced with the pyrovalve which was deemed much simpler and more reliable.

Okay that sounds like a solid piece of advice. So pyrovalves are simpler than solenoid valves? I had heard that they were more reliable before but I though they were more complicated than a solenoid valve?

 

[dhbarr]

Okay that sounds like a solid piece of advice. So pyrovalves are simpler than solenoid valves? I had heard that they were more reliable before but I though they were more complicated than a solenoid valve?

I think maybe you're imagining some kind of mechanism involving moving parts. The pyrovalve most people are talking about is literally a slug of hard propellant with an oxidizer-compatible barrier on one end.

 

[rocket_troy]

Cheers, the animation does work by the way. So I am guessing the brown is your solid charge?

Yup.

TP