Pneumatic Valve for Shutdown cylinder - Question

[veggie]

Fail Safe Engine Control - (Controller power failure or air leak causes engine to stop)

Much like locomotive train brakes, I wish to have my engine fuel and decompression pneumatically energized (activated) when the engine is in run mode.
Removal of the air pressure will result in a spring returning the decompression lever and fuel rack to the off position.
Any interruption in my control power to the air solenoid valve will result in an automatic shutdown.
Other conditions such as over-speed and normal engine kill can be handled easily with a switch or control relay wired to the air solenoid valve.
I know that some of our members have done this (quinnf and BruceM come to mind).

My question: ENGINE KILL
When the system is de-energized (electrical power removed from the air solenoid valve) to attempt an engine kill, how does the pressure bleed from the cylinder once the NORMALLY CLOSED air solenoid valve.?  Pressure will still be in the system preventing the ram from returning to rest.
How have others dealt with this condition?

Veggie

[playdiesel]

I have no familiarity with the particular systems you mentioned but normally the control valve will bleed the system pressure  from the load side when it returns to the normal position.  This works rather slowly,  if the system requires quick release of pressure then dump valves or sometimes called quick release valves are installed between the operating valve and the work. These work by sensing pressure either side of them. If pressure from the valve is equal or more then the cylinder side pressure they quick release valves remain closed. However the instant that the cylinder or work  side is higher than the valve side they open to "exhaust" and dump line pressures to zero. A common application of them is in truck brakes. When a driver applies the parking brake OR releases the foot brake quick release valves dump the air quickly making that sound we are all familiar with. They are made in small sizes for air operated industrial machines, just like you will need for your set up. 
Punch in "quick release valve" on an Ebay search for a long list of them for sale.
Butch

[Jens]

Similar idea as Butch ... have a normally open valve, electrically operated, on the pneumatic cylinder. If power is present, the valve is closed, if power is absent, the valve opens. So, if an error condition is present you drop power on both the air actuator valve and the release valve and presto .... I think ....

[BruceM]

Vegge-  there are special air solenoid valves which have air bleed when closed, to allow single action pneumatic cylinders to retract. Sometimes they are listed on ebay as three way valves, but they are really a special type of valve for this purpose.

As you may remember, my Lister CS system is all pneumatically controlled, including remote starts and auto shutdown on various faults like low oil, low/high speed, vibration.

I try to avoid normally pressurized cylinders for operation due to air leakage.  You will have some leakage at the cylinder and will have to be very careful with your plumbing to the solenoid valve.  You will also have some leakage at the regulator.  It is the downside of pneumatics...which otherwise is a great and affordable way to get powerful actuators.

My design philosophy was this-  my monitoring system is all the protection I have, and it is a vast improvement over nothing.  If it fails, I am back to the manual mode of operation.  So I chose to not have failsafe of my safety monitoring system but rather implemented it to use as little air as possible but mostly be as simple as possible.  I do not regret this design choice.

Best Wishes,
Bruce

[mobile_bob]

veggie

i follow what it is you are wanting to do,  and you might look into what is offered for hd trucks for fan control
solenoids and such,  often times hd truck stuff can be had pretty reasonably and is very robust and long lived.

another option, one i use to do at least part of what you are looking for is this

http://www.ebay.com/itm/New-Fuel-Shut-Off-Solenoid-For-94-98-5-9L-Dodge-Diesel-Cummins-3931570/171820279817?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D39007%26meid%3D4d96aee8ded74feb9f3790bd124a2827%26pid%3D100005%26rk%3D3%26rkt%3D18%26sd%3D150726015045

these units have come down in price to a fraction of what they were even 5 years ago!

i use two of these on the s195 trigen unit,  one is used to pull the governor spring from no fuel to low idle (1000rpm) and the other pulls the same governor spring to high idle (1800rpm) via a pair of sash chains.  i mounted them side by side
and attached a short section of sash chain to connect to the governor spring, that way when one solenoid is disengaged its chain falls slack, while the other pulls tight when activated, both slack = no fuel position and the engine dies.  the solenoids are setup and the slack is adjusted to get the exact rpm i want with the requisite solenoid fully retracted... these have to be fully retracted else they will burn out the pull in winding and get to the hold in winding which disconnects the pull in winding.   loss of power to either solenoid results in the spring going slack and the engine rack going to no fuel position.

i think one of these could also be used to pull the compression release as well, but would have to have power to the solenoid in order to activate the compression release.

fwiw
bob g

[veggie]

Thanks everyone for your input.

Bob

I notice the fuel rack solenoid you suggested has 3 wires. Does the pull-in winding have to be energized separately from the hold-in winding ?
(Meaning a momentary timer control for the pull-in)
Or does the rod travel switch the windings from "pull" to "hold" as it progresses down the bore?
Why 3 wires ?

Veggie

[mobile_bob]

Veggie

good catch, i am not sure of why this one has three wires, let me look further

the units i use are two wire, and have a set of contacts built internally that switch over to the hold in winding
once the plunger makes full travel

let me get back to you

bob g

[mobile_bob]

here is a two wire unit, or two connector

http://www.ebay.com/itm/New-Fuel-Shut-Off-Solenoid-replace-Lister-Petter-Solenoid-SA-34053-/181941048564?tfrom=171820279817&tpos=top&ttype=price&talgo=undefined

or

http://www.ebay.com/itm/NEW-FUEL-SHUT-OFF-SOLENOID-replace-FOR-LISTER-PETTER-SOLENOID-366-07197-SA-3405T/271834527532?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D39007%26meid%3D8776ec9a3569458b9d62dc27862b43d5%26pid%3D100005%26rk%3D1%26rkt%3D18%26sd%3D181941048564

i am not sure about the 3 wire, it might be that the 3 wire unit has one wire (black) that goes to ground
another wire that goes to switched power (ignition) and the other to the starter solenoid or switch start position
in order to have the pull in coil energized.  i bet it could be used, but why use it when there are two wire units available.

note**  the third wire apparently is an auxilliary wire, i seem to recall some small cummins using that to tell the chassis computer or some other circuit such as the intake heater that the fuel solenoid is activated... i think the three wire unit could be used for our purposes using only two wire, but if there is a 2 wire alternative maybe we just use that one.  however there might be a use for the auxilliary wire for those that like to tie this in with their automation systems design, there it might be useful as an easy check of state of the solenoid.

bob g

[BruceM]

These affordable fuel rack solenoids look very interesting, Bob.  What is the approximate closing and holding force they can apply?

[mobile_bob]

i wish i could tell you what the pull in force is exactly, i can only say that the pull in is enough
that it is very hard to hang on to the darn things, that is if they are setup to have ~1/2-3/4" travel
as for hold in, you can pull it back, but it is fairly hard to do so.

i know this is not very scientific and very subjective

my thinking is the hold in is at least 3 lbs, and the pull in maybe 10lbs

never really measured either, so i may be way off.

they have no problem pulling in the governor spring on an s195changfa, and no issue at all holding
the spring extended either, even when i try to add more spring force they seem to hold just fine.

fwiw
bob g