Inline Check-Valve breakaway pressure for CNG

[josch]

Does anybody know what the recommended cracking pressure should be for a check-valve that mounts between the filler receptacle and the cylinder on the filling circuit should be? I used this one: http://www.swagelok.com/search/produ...S-CHS4-10-SC11
which has a 10 psi cracking pressure, and it sounds like it might be fluttering at times due to minor pressure harmonics in the line while running as the pressure in the system on the main supply circuit drops vs pressure in the filler circuit (between filler receptacle and check valve). I am thinking I may need a check valve with like say a 50 psi cracking pressure or more, but if somebody knows the official spec on this I would definitely like to adhere to that, before I spend $45 bucks on a check valve.

[larrycng]

Re: Inline Check-Valve breakaway pressure for CNG

Josch,
I don't of any requirement on check valve "cracking pressure" (unless they are vehicle manufacturer or kit manufacturer specific). I've use check valves with 10 psi cracking pressure and get the same chattering when the fuel is close to equalization. I wouldn't waste the money. Besides 50 psi cracking pressure would mean that you would be getting less fuel since you would need to have over a 50 psi differential between tank pressure and fuel dispenser pressure to get fuel to flow to the tank.

Hope this helps

Larrycng

[CraziFuzzy]

Re: Inline Check-Valve breakaway pressure for CNG

Any check valve you get is going to chatter near end of fill, as the rate of fill drops towards zero. When mine starts chattering, if it annoys me, I just stop filling then. With a 10psi check, if you are chattering, you're probably only gonna get a couple more pounds in the tank anyways.

[josch]

Re: Inline Check-Valve breakaway pressure for CNG

NO, mine does not chatter at all when filling, it just chatters while driving, when you sink into the throttle. I seems a slight bit less chattery as the regulator has been breaking in, I think it might be less jerky. I am only guessing here, but this is my theory.

Maybe if I just pack insulation all around in that compartment around those hoses I wont hear the noise

[josch]

Re: Inline Check-Valve breakaway pressure for CNG

Josch,
I don't of any requirement on check valve "cracking pressure" (unless they are vehicle manufacturer or kit manufacturer specific). I've use check valves with 10 psi cracking pressure and get the same chattering when the fuel is close to equalization. I wouldn't waste the money. Besides 50 psi cracking pressure would mean that you would be getting less fuel since you would need to have over a 50 psi differential between tank pressure and fuel dispenser pressure to get fuel to flow to the tank.

Hope this helps

Larrycng

Yeah this thought had crossed my mind about not getting a full fill because of the high breakaway psi

[Franz]

Re: Inline Check-Valve breakaway pressure for CNG

There has never been an ordinance on a requirement for cracking pressure requirements. All the cracking pressure is there for is to insure that the ball is fully seated at low pressures.

A fill check valve should not chatter while driving, only while filling. Any chattering may be from a primary pressure regulator not able to maintain its droop (the ability to maintain a constant outlet pressure in reference to its inlet pressure while under load).

Most vehicles have its fill check valve integrated into the fill nozzle. A regional ordinance may require a separate check valve.

Franz

[CraziFuzzy]

Re: Inline Check-Valve breakaway pressure for CNG

You are getting chatter from your filling check while driving? Sounds like a problem with the check, more than a cracking pressure issue. You should have anywhere between 3600 and 150 psi reverse pressure on that valve when not fueling, so it shouldn't even be close to opening.

[josch]

Re: Inline Check-Valve breakaway pressure for CNG

Yeah, but if your system-side pressure is say 3400psi and dropping as you are driving, and then the 3 ft section of tube between the check valve and the filler receptacle still were to have 10 psi higher than that at all times, then whenever you have a drop on the system side, of 10psi lower than the filler side, then the ball will lift off the seat and could easily bounce whenever you have small surges in system pressure if the regulator is not smooth in letting off high-side pressure to the low-side regulator. I also notice the noise is more there when my variable cylinder switchover is activating CNG to just cylinder-at-a-time as it activates cylinder 1, then a second later, cylinder 2, and 3, then 4, etc. This causes an irregular draw on the low-pressure fuel rail which in turn causes a surge on the high-side as the regulator is trying to keep the low-pressure rail at a constant 1.5 bar. This surge in the high-pressure line under load also makes that rattle sound more pronounced until all the cylinders have switched to CNG and the low-pressure rail has a nice evenly timed draw from each injector.

The only other thing back there that could be making the noise, is my electric in-line solenoid valve which is mounted about 8 inches out of the cylinder valve on the line that goes to the front of the car. This solenoid is not a motor-type valve but likely a needle/seat type sliding valve, but is designed for this application so I had doubted that it could be what is bouncing. I just need to get my wife to drive while I go back there with my mechanic's stethoscope and pinpoint which of the 2 things is making the racket. I had just assumed it could only be the check valve since it sounded more logical to me that this could bounce since it only has a 10 psi spring in it, and with system pressure dropping while driving etc.

Thanks for all you guys' suggestions so far

[josch]

Re: Inline Check-Valve breakaway pressure for CNG

Well, I just tested it with my stethoscope and it is definitely the check valve that is rattling. I suppose if it were mounted like an inch or 2 from the filler receptacle it probably wouldn't have this problem, but I had purposely wanted the check valve mounted within 6 inches of the tank because the filler is on the rear bumper, and I figured that if I ever got rear-ended and it severed the line that the check valve would be safe inside the cabin right near the tank, and it would protect the system from any discharge if that filler line got damaged.

I guess I could try a stiffer spring in it to see if it keeps it from rattling. Even a 20 or 30 psi spring might be enough not to rattle from minor line surges.

[Amfuel]

Re: Inline Check-Valve breakaway pressure for CNG

Since your receptacle has a check ball in it, it sounds like your check valve would be at equilibrium, hence the rattle. Would any spring stop the rattle? With the recep on the back bumper the check valve is a good safety. I would try and dampen the noise. Wrap the valve and line or turn up the music, get glass packs, etc.

Fuel Maker has a blow down tank in which the gas pressure is relieved into at the end of filling. The blow down pressure can reach 50psi as that is low enough to enable disconnecting the hose without too much effort. The length of hose and volume of gas and blowdown tank size all figure into the disconnect pressure.

[josch]

Re: Inline Check-Valve breakaway pressure for CNG

Well I already got a Flowmaster on it.

NFPA-52 says you need a second in-line check valve in case the one in the filler receptacle gets dirt in it, then it is less likely to leak out. Plus I wanted it there in case I ever got rear-ended then it would not empty my tank right there.

Also, the CNG fuel stations like Flying-J's also have the valve to bleed off pressure, but it just bleeds pressure in the hose between the pump's solenoid and the filler receptacle's check ball. Not beyond that.

Maybe I will try to wrap some insulation around it. I do think a stiffer spring though would keep minor pressure surges and fluctuations in the line from rattling it as much. I think 10 psi might be too weak so if the pressure bounces even that amount the check ball tends to follow that. That why I was curious if anybody knew what spec on some OEM car was.

Maybe I will take a brass center punch and tap on the filler receptacle's check ball to relieve the pressure in that hose section and check to see if the noise goes away for sure thus proving my theory.


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