Hi All,
This manouver should be always done before opening any part of the gas system. Ok, there are many many valves in the system, and I would not bother to do it if I was changing just the gas injectors to the intake manifold, but unless you are 100 % sure of the safety, do it.
Next about the liability: I can only tell here how I have done the procedures to my car, because I know the system set-up pretty well. I have opened it many times and am still writing here. So if you have a similar car (different year models can have different systems), and do the same things that I did, maybe also you will not blow up your car and yourself with it. So let's tell here how have we done the things, and then everybody decides theirselves, whether they are confident enough to do self-service with their cars.
My car is a Volvo V70 Bifuel from year 2000. It has one big gas tank in behind the rear seat backrest. Basically the operation is easy: start the engine, let it run with gas for a moment, close the manual shut-off valves from the gas tank, let the motor consume the rest of gas in the system and finally die. Nothing complicated. The hard part is to be able to operate the shut-off valves. When you have completed the other things that required the gas system to be depressurized, and are sure that every part of the system is properly assembled and will not leak, DO NOT FORGET TO OPEN THE MANUAL SHUT-OFF VALVES AGAIN, if you wish to drive again with gas. I forget it every freaking time ; )
To reach to the valves, first flip down the backrests and the cover dressing. Screw off (anti-clockwise) the round plastic shield from the passenger side of the tank end. Be careful when the shield goes off from the threads, just slide it away as much the electric wires allow, to be able to reach the two closing valves. The closing valves are operated with 3/16" hex bit, these little hex socket pits are located in the centers of the two big hex bolts which sit on the exposed valve unit. So when you have tested that you can actually operate the valves, you can proceed with the above mentioned steps. Actually, I think that it would be enough to close only that valve which leads the gas to the engine, but I have always closed them both to be sure. Just make sure that the motor dies.
From what I've heard about newer Bifuel models, they have slightly more complicated systems with those 2 little extra tanks. But I think the little tanks are upstream from the big tank, so basically shutting the both valves of the big tank ought to do the job. I don't know should the little tanks be manually closed too (only one valve per tank)? Maybe it's safer to close them too when the motor has died? I've also heard that with 2002 or older models, a connector at the big gas tank strap (going to the magnet valve?), should be first disconnected to kill the motor, before closing the big tank manual valves. With the models 2003 and newer, the same thing would be done by disconnecting a relay from position RMI 17, located somewhere in the trunk. Someone else please correct me, if I have understood something wrong about these newer models.
Best Regards, Hewey
...U gotta fight, for your right, to cruise on...
Volvo Bifuel gas system depressurising
Volvo Bifuel gas system depressurising
Last edited by Hewey on 2009-05-11, 10:22, edited 1 time in total.
När det gäller de nyare modellerna, 2002 och framåt (?), så tror jag att det är väldigt mycket enklare att släppa på trycket. Min mek skruvade ur någon liten skruv på gasregulatorn, eller om det var gasfördelaren, så att det började pysa som sjutton. När han såg min något bleka uppsyn sa han: "Det är lugnt, säkerhetsventilen bak i tanken slår snart till. Så här gör man alltid när man ska byta grejer i gassystemet som sitter i motorrummet.". Och mycket riktigt, efter ett tiotal sekunder slutade det pysa. Därefter började meken skruva ur anslutningarna till regulatorn som skulle bytas! 
Mvh
/Fred
Mvh
/Fred
Volvo V70 Bi-Fuel Manuell -02
Trevlig att höra olika metoder, speciellt sådana som yrkesmän användar. När vi amatörer först förstår varför yrkesmän gör sakerna som de gör, vi kan kanske också göra på samma sätt. Din mekaniker måste känna alla årmodellerna och därför han kan göra tryggt som du beskrev. Han vet att där finns en säkerhetsventil, litar på det och låter gasen bli fri direkt från systemet. Kanske det är mycket snabbare att göra så. Jag tror att det var en skruv på gastryckregulatorn som han öppnade. Före regulatorn i gaslinjen existerar högtrycket (som bäst över 200 bar) som är den huvudsakliga risken och måste vara avlägsnat. Efter en fungerande regulatorn trycket är inte längre mera än 1 bar, som är en mycket mindre risk.
Jag vet inte om min system har en likadan säkerhetsventil, men jag ska utforska det. Om någon gång jag har inte tid att avlägsna trycket på traditionell sätt, det skulle vara roligt att kunna göra det snabbare också.
Lite fri gas i motorrummet är kanske inte en stor risk, speciellt när motorhuven är öppen. Det måste vara en liten stängd rum och stor läcka innan metanhalt ökar tillräckligt för att vara kapabel att antända. Jag körde många månader utan problem med en ganska stor läcka i motorrummet och det läcker ännu litet från stegmotorn. Naturligtvis är metanutsläppet skadlig för naturen, så för att vara miljövänlig, man vill försöka att bränna alla metanen med motorn till koldioxiden, som är en mindre växthusgas.
Mvh, Hewey
Jag vet inte om min system har en likadan säkerhetsventil, men jag ska utforska det. Om någon gång jag har inte tid att avlägsna trycket på traditionell sätt, det skulle vara roligt att kunna göra det snabbare också.
Lite fri gas i motorrummet är kanske inte en stor risk, speciellt när motorhuven är öppen. Det måste vara en liten stängd rum och stor läcka innan metanhalt ökar tillräckligt för att vara kapabel att antända. Jag körde många månader utan problem med en ganska stor läcka i motorrummet och det läcker ännu litet från stegmotorn. Naturligtvis är metanutsläppet skadlig för naturen, så för att vara miljövänlig, man vill försöka att bränna alla metanen med motorn till koldioxiden, som är en mindre växthusgas.
Mvh, Hewey
Hi again Fred,
I wonder why I did not thought earlier about the system setup enough. Of course there is the magnet valve in the gas tank, which is always mechanically closed, when it has no electricity. So why not count on it when depressurizing the system? Instead of using the manual shut off valves, disactivating the magnet valve while the engine runs on gas, will get rid of the gas pressure in the system, and then the motor dies finally. Disconnecting the magnet valve: Years <- 2002 you disconnect the connector of the magnet valve (somewhere near the tank strap), and from 2003 -> you disconnect the relay at RMI 17 from the trunk.
If you don't care about the atmosphere, you can depressurize the gas system (the engine stopped of course -> magnet valve not recieving electricity) basically just opening the system and letting the gas flow out, which is what your mechanic did. My pressure regulator (year 2000, the older system) has a test plug in it, and it seems that also the newer regulator has one too. Although it is highly unlike that the magnet valve should have somehow get electricity during the service, I would feel safer when it is disconnected. And if you take the time to disconnect it, why not make the depressurizing the proper way in the first place.
If you want to be absolutely sure that the gas tank pressure will stay inside the tank, then you can also manually shut the gas tank outgoing manual valve. But as it is quite hard to reach in most cases, why would you not trust the magnetic valve, especially if you have disconnected the electricity from it. I haven't bothered to close the manual valve anymore, why would the magnetic valve suddenly fail during the service, if it has been operating normally for years and years? And if you also run the tank as empty as you can before the service, the maximum pressure in the system is about 10 bar, which is not so very dangerous anyway.
Regards, Hewey
I wonder why I did not thought earlier about the system setup enough. Of course there is the magnet valve in the gas tank, which is always mechanically closed, when it has no electricity. So why not count on it when depressurizing the system? Instead of using the manual shut off valves, disactivating the magnet valve while the engine runs on gas, will get rid of the gas pressure in the system, and then the motor dies finally. Disconnecting the magnet valve: Years <- 2002 you disconnect the connector of the magnet valve (somewhere near the tank strap), and from 2003 -> you disconnect the relay at RMI 17 from the trunk.
If you don't care about the atmosphere, you can depressurize the gas system (the engine stopped of course -> magnet valve not recieving electricity) basically just opening the system and letting the gas flow out, which is what your mechanic did. My pressure regulator (year 2000, the older system) has a test plug in it, and it seems that also the newer regulator has one too. Although it is highly unlike that the magnet valve should have somehow get electricity during the service, I would feel safer when it is disconnected. And if you take the time to disconnect it, why not make the depressurizing the proper way in the first place.
If you want to be absolutely sure that the gas tank pressure will stay inside the tank, then you can also manually shut the gas tank outgoing manual valve. But as it is quite hard to reach in most cases, why would you not trust the magnetic valve, especially if you have disconnected the electricity from it. I haven't bothered to close the manual valve anymore, why would the magnetic valve suddenly fail during the service, if it has been operating normally for years and years? And if you also run the tank as empty as you can before the service, the maximum pressure in the system is about 10 bar, which is not so very dangerous anyway.
Regards, Hewey
Hewey.. I think those magnet valves are not opened until the system swiches over to run on gas? You can hear a "clonking" sound just before the system switches over to gas, i believe this sound is from the magnet valves.. So im not 100% they open directly when you start the car...
A technichan also told me that Volvo is the only manufacturer that swiches over to running on gasoline when there still is a lot of gas in the tanks. Other brands uses more of the gas pressure before the valves closes. I dont know if he told me that volvo closes at 8 bar.. or if it was 18 bar? .. hmm .. He said that you could get 10-20km further if you just change those valves (the magnetic ones?) and replaces them with other that closes later at a lower pressure...
Well this is not an issue for me anymore... since my car has done its 120 000km now and in 2 weeks i change it to an VW Passat
A technichan also told me that Volvo is the only manufacturer that swiches over to running on gasoline when there still is a lot of gas in the tanks. Other brands uses more of the gas pressure before the valves closes. I dont know if he told me that volvo closes at 8 bar.. or if it was 18 bar? .. hmm .. He said that you could get 10-20km further if you just change those valves (the magnetic ones?) and replaces them with other that closes later at a lower pressure...
Well this is not an issue for me anymore... since my car has done its 120 000km now and in 2 weeks i change it to an VW Passat
Passat Variant TSI Ecofuel DSG -10 | 
Volvo S60 Bi-Fuel Aut.-06 (Såld)Hi Taz,
Yes, I can hear also the magnet valve opening in the gas tank. I think the magnet valve in the gas tank opens a little bit earlier before the switch to allow the pressure regulation to stabilize. Then just before the switch the magnet valve in the gas distributor opens and for a moment both fuels are fed to the intake so the switch goes smoothly. When petrol feed stops, the motor run can hesitate for a moment before stabile gas run is achieved.
The reason to use (or to just count on to the fact that the magnet valve is always closed when it doesn't have electricity) the tank magnet valve in the depressurization is because it is easier and faster to operate it than to physically screw the manual valve. If someone does not feel safe just with the magnet valve, he/she can always also use the manual valve too for maximum security.
The minimum tank pressure limitation (what ever it is then) might be set in order to maximize the life of the composite materials of the big gas tank. If all the stress would be periodically taken away from it, the strength of the materials could be weakening faster. If the composite tank is changed after it's expiration date to a metallic tank, maybe then it would be safe to modify the system to allow smaller minimum pressure limit. My composite tank is expiring in 2013, but the way it looks like (air bubbles and cracks in the coating), I think I'm replacing it pretty soon for safety. You guys with the tank outside the car body are much more safe in that way. I will feel kinda shrunk if the car cabin should someday decide to pressurize to about 200 bars...
Good luck with the new car, I hope VW will be even better. I think I'll stick to my old reliable V70 still for a long time. If nothing else, it has been reliably in keeping my hands dirty : )
Regards, Hewey
Yes, I can hear also the magnet valve opening in the gas tank. I think the magnet valve in the gas tank opens a little bit earlier before the switch to allow the pressure regulation to stabilize. Then just before the switch the magnet valve in the gas distributor opens and for a moment both fuels are fed to the intake so the switch goes smoothly. When petrol feed stops, the motor run can hesitate for a moment before stabile gas run is achieved.
The reason to use (or to just count on to the fact that the magnet valve is always closed when it doesn't have electricity) the tank magnet valve in the depressurization is because it is easier and faster to operate it than to physically screw the manual valve. If someone does not feel safe just with the magnet valve, he/she can always also use the manual valve too for maximum security.
The minimum tank pressure limitation (what ever it is then) might be set in order to maximize the life of the composite materials of the big gas tank. If all the stress would be periodically taken away from it, the strength of the materials could be weakening faster. If the composite tank is changed after it's expiration date to a metallic tank, maybe then it would be safe to modify the system to allow smaller minimum pressure limit. My composite tank is expiring in 2013, but the way it looks like (air bubbles and cracks in the coating), I think I'm replacing it pretty soon for safety. You guys with the tank outside the car body are much more safe in that way. I will feel kinda shrunk if the car cabin should someday decide to pressurize to about 200 bars...
Good luck with the new car, I hope VW will be even better. I think I'll stick to my old reliable V70 still for a long time. If nothing else, it has been reliably in keeping my hands dirty : )
Regards, Hewey