In reverse order, the swage fitting. You have to drill through the fitting
past the tubing stop so your dip tube can slide freely through the fitting
to the desired depth.
The hybrid motor purge check valve should be connected to the head/injector
end of the CC. Your reg. will be upstream some distance with the 2x sol.
valve between the check and reg. Before the test you set the reg at 5-10%
below expected chamber pressure,Pc. When your motor fires and reaches rated
Pc the 2x sol valve is energized but no gas can flow because of the back
pressure of the motor's Pc. When the motor stops firing as Pc drops 5-10%
below its rated value the check valve unseats and your purge ensues. This
system allows for a smooth hand off of Pc to purge with no interim drop in
gas flow through the motor.
It's a great but simple system that leaves a nice predictable Pc instrument
trace.
Some motors exhibit combustion instability so filling the Pc
transducer line with grease protects the ducer from heat damage and put
your purge check far enough away from the motor to protect it too as you
can't put grease in it.
Hope that helps, more question are welcome,
Ken
On Tue, Jan 5, 2021 at 8:41 AM elias Aoubala <eliaslina88@xxxxxxxxxxxxx>
wrote:
Thanks Ken for the reply,
Apologies for my late reply as I was a bit busy yesterday but I wanted to
ask for you to maybe explain a bit more on the use of the regulator to
purge as I am struggling to understand how you suggested to use the
regulator with the check vales and two solenoids. Could you try and explain
a bit more if possible as I think due to my lack of experience is impeding
me from understanding it.
I have looked into the Swagelok bored fittings on your advice for the dip
tube and it does look extremely interesting so I thank you for the
suggestion.
Cheers again,
Elias
*From: *roxanna Mason <rocketmaster.ken@xxxxxxxxx>
*Sent: *04 January 2021 18:43
*To: *arocket@xxxxxxxxxxxxx
*Subject: *[AR] Re: Regarding Hybrid Rocket Feed System Design
A health purge will do wonders. Have a regulator set maybe 5-10% below
your Pc with a check valve and 2x sol. valve between the reg and your motor
When you fire the motor energize the 2x sol. valve. purge gas will not
flow against chamber pressure higher than the purge reg set point. At end
of burn once the motor Pc drops it hands off to the purge. You get an
instant transition from Pc to purge, works great.
Dip tube? We're having a similar requirement on our 1.5KLbF LOx/Kero
rocket. I proposed a swagelok fitting with the dip tube slid down to the
desired liquid level then swage the tube. If a level change is needed
either cut the tube for a higher level or change out to a new swage/tube
assembly. You can also use brass hardware store compression fittings for
low budget easy access supply.
Not sure what your other question meant with a reg ball valve and nitrous
but be careful with the nitrous, don't let it cavitate or experience high
turbulence in a duct or get contaminated. Nitrous killed my friend and
colleague at Scaled Composites in 2010 along with two others.
Good luck,
Ken
On Mon, Jan 4, 2021 at 8:06 AM elias Aoubala <eliaslina88@xxxxxxxxxxxxx>
wrote:
Hey Guys,
A while back I started a thread here about initially designing my feed
system for a Hybrid Nitrous Oxide- HTPB engine. I think I’ve finally come
to final possible design and I wanted to post it here to get some opinions
from others on the design.
Overall I had a few questions I wanted to voice about the current design
of the feed system I have. Firstly My question is as to how do I prevent a
backflow of combustion flames through the injector line once it is shut off
after ignition. My first Idea was to implement another Flame back Arrestor
and/or have flame back arrestors on each line(main and ignitor)- however I
think there might be another solution which I am trying to figure out.
For the purge/fill vent (which I intend to use so I can use a dip tube on
my fill tank instead of gravity filling), I was initially thinking to put
it at the 4 way fitting above the tank which would simplify the tank design
significantly however I was thinking this would just lead to the liquid
flow to just exit thought the 4 way fitting to atmosphere instead of
actually entering the tank. Im not so sure about the design decision so I
would love to here thoughts about it.
Regarding the actual Dip tube for my fill tank- I’m getting my tank bought
from a third party and I wanted to know is their somewhat of a universal
method of building a dip-tube (or generally how do you build a dip tube for
third party tanks) and how do I do it (no experience with dip tube design).
Another point Id like to mention is the positioning of the actual back up
regulator, would I require anymore regulators for use between the actual
automated ball valves for Nitrous Oxide?
As you clearly can see from this post, I am still new to this so any
help/advice at all would be very much appreciated given how confusing this
feed system stuff can get and I really do appreciate the amount of help you
guys have given me already.
Many Thanks again,
Elias