A rocket engine purge valve injects gas immediately downstream of a main
propellant valve, in the length of line that is normally open to the air
through the engine. The purge gas can be taken from the same regulator
as the tank press source, with a check valve in line with the press
valve to prevent sucking gas from the propellant tank. (This is another
good reason to have two independent bottles for the LOX & fuel systems,
no way to contaminate the propellant lines.)
The two purge valves feed ~50 psi relief valves that exhaust directly at
the downstream face of the main valve balls (assuming ball valves).
The purges are turned on first, a fraction of a second before the
igniter is started. Not much gas is used because the gas flow stops as
soon as the engine lights and pressure builds in the lines.
The engine runs smoothly because normal propellant flow is at higher
pressure than the purge relief valve outlet, and propellants can't flow
backward into the purge because that is slightly above tank pressure.
At shutdown, the main valves close and the purges flow as soon as line
pressures drop to tank-50 psi, blowing the trapped O&F out through the
engine. Cross-contamination of the injector galleries is prevented.
About a second after engine stop, the purges can be turned off. The
engine is left clean and dry.
Aluminum is fully compatible with ethanol, no need to change it out.
Both run tanks should be hydrotested to 1.5x maximum expected operating
pressure before assembly into the stand.
All press, vent, pre, main, and purge valves should be remote
controlled. Fill valves can be manual, and a manual LOX Vent valve is
useful for leaving an unattended stand in a safe condition to allow
boiloff of remaining LOX overnight.
Bleed valves are generally not needed- just close the GHe and GH2 bottle
valves, then run tank press and vent at the same time to flow all
trapped gas through the regulators.
Prevalves upstream of the main valves allow emergency shutdown even if
the main valves are damaged or stuck open.
Check valves between main valves and the engine are not needed. If your
engine does hard start, the check valves won't react as fast as the
pressure wave travels. Use interlocked ignition (a pressure switch on
the igniter detects operation, enables main valves) to prevent hard starts.
On schematics I find it useful to show LOX in green, Fuel in red, inert
gases in blue and black. Labels can applied to all lines on the stand to
prevent dumb cross-connection mistakes.
At XCOR we've always tested engines horizontally, never a crisis due to
fuel pooling.
Doug Jones, Chief Test Engineer
XCOR Aerospace
1325 Sabovich
Mojave CA 93501
(661) 824-4714 x117
cell 661 313-0584
On 4/20/2016 3:01 PM, Kyle Meeuwsen wrote:
All,
Thank you very much for the responses. There has already been a lot of
good learning here. Below are some of my responses and then some
additional questions in no particular order:
The Ethanol tank is currently aluminum.... Last year's senior design
team acquired it and the thought was that the Ethanol will not be
present in the tanks long enough to cause issues. I am inclined to
replace it with a proper material since I am not sure what the effects
of Ethanol residue on aluminum is over time. I am not sure on the
material for the LOX - I will look it up when I get home. I believe the
tank was previously used for oxygen in industry.
For the Ethanol and LOX manifolds, I have a line coming in to a 4 way
port with a pressure relief valve, a solenoid, a bleed/purge valve, and
soon a burst disc.
- What is the different between a purge valve and a bleed valve, unless
synonymous?
- Is a bleed/purge valve a manual valve? It seems that this defeats the
purpose of remote system pressure relief for disarming.
- Please please what is the different between a pressure relief valve
and a purge valve?
- Is the solenoid attached to the top of the LOX and Ethanol tanks
venting to atmosphere intended to be the primary means of remote
pressure relief to achieve disarming? Is this what I would call my vent
valve?
Ben, you stated:
"* You're going to want purges to clear out the lines to the engine
before and after running. Typically they come from above the tank
press valve, through an orifice and a solenoid valve and a check valve
or two, and are injected on the downstream side of the engine run
valve."
On the statement: You're going to want purges to clear out the lines to
the engine before and after running."
Here is "purges" a noun as in a purge vent, or a verb as in the process
of purging?
On the statement: Typically they come from above the tank press valve,
through an orifice and a solenoid valve and a check valve or two, and
are injected on the downstream side of the engine run valve."
- Is "they" referring to the verb of purging?
- What is the "tank press valve"?
- Is the "orifice and a solenoid valve" possibly part of the main LOX
pressurant line, upstream from the LOX tank inlet?
- When you state "and are injected on the downstream side of the engine
run valve" are you referring to injecting the LOX pressurant gas into
the downstream side of the engine run valve?
- What is the engine run valve?
Lastly, how bad is it if the team wants to mount the engine to the stand
such that the exhaust outlet is parallel to the ground (mounted
horizontally). I have concerns about fuel pooling following testing.
Thank you many many times for the information. This has been a huge help
so far.
I will post pictures of the test stand and components tonight and link
them to this thread for those interested.
This is a very great group of people.
Best,
Kyle
On Wed, Apr 20, 2016 at 2:23 PM, Wyatt Rehder <wyatt.rehder@xxxxxxxxx
<mailto:wyatt.rehder@xxxxxxxxx>> wrote:
Russ,
What flavor? LN2 ice creme is literally one of my favorite things...
I've had some pretty good luck with caramel.
Wyatt Rehder
On Wed, Apr 20, 2016 at 12:29 PM, Russell Blink <russ@xxxxxxxxxxxx
<mailto:russ@xxxxxxxxxxxx>> wrote:
> I did just make some LN2 ice cream in our work kitchen and got a
bit light headed, just turned on the AC and all was good.
> (some ventilation is good)
>
> Russ Blink
> Exos Aero
>
>
>
> -----Original Message-----
> From: arocket-bounce@xxxxxxxxxxxxx
<mailto:arocket-bounce@xxxxxxxxxxxxx>
[mailto:arocket-bounce@xxxxxxxxxxxxx
<mailto:arocket-bounce@xxxxxxxxxxxxx>] On Behalf Of Ben Brockert
> Sent: Wednesday, April 20, 2016 11:57 AM
> To: arocket@xxxxxxxxxxxxx <mailto:arocket@xxxxxxxxxxxxx>
> Subject: [AR] Re: Portland State Aerospace Society
>
> You're not going to suffocate by taking a sniff of nitrogen. Even
a full lungfull of pure helium or nitrogen won't kill you.
>
> On Thu, Apr 21, 2016 at 12:44 AM, Robert Steinke
<robert.steinke@xxxxxxxxx <mailto:robert.steinke@xxxxxxxxx>> wrote:
>>
>>
>> On Wed, Apr 20, 2016 at 10:13 AM, Paul Mueller
>> <paul.mueller.iii@xxxxxxxxx <mailto:paul.mueller.iii@xxxxxxxxx>>
>> wrote:
>>>
>>> (swish it around, blow it out with dry air until you can't
smell the
>>> alcohol smell anymore on the outlet).
>>
>>
>>
>> If you are sniffing the outlet you absolutely MUST use dry AIR
as Paul
>> says, not dry NITROGEN so you don't suffocate yourself. I thought
>> this was worth some capital letters.
>>
>
>
>
