How much air pressure do you run in your accumulator?
accumulator air pressure?
2 reading
mcintosh
41 - 59 of 59 Posts
Joined
·
7,351 Posts
I had timed out on the edit deal, sorry again.
Your Pal, Gary
Your Pal, Gary
Joined
·
17,527 Posts
Originally Posted by bottlefed1 
This is true but what I think montys55 was illuding to is that if you set the accumlator pressure to 100 and you only have 80 psi of oil pressure your not likely to move the accumulator piston any hence no oil stored. Naturally this would be an extreme case but say you set it at 20 and with the piston all the way back the pressure rose to 50 and your idle oil pressure on the top end after lifting and coasting at idle was only 30 lbs...so now the accumulator piston has pushed out most all of the oil and you make the turn off and it drops to near zero and you only have a little oil left in reserve. I assume this is why they suggest setting the lower setting for the average Joe who may really need this sort of band aid for a poor oil system.
This is true but what I think montys55 was illuding to is that if you set the accumlator pressure to 100 and you only have 80 psi of oil pressure your not likely to move the accumulator piston any hence no oil stored. Naturally this would be an extreme case but say you set it at 20 and with the piston all the way back the pressure rose to 50 and your idle oil pressure on the top end after lifting and coasting at idle was only 30 lbs...so now the accumulator piston has pushed out most all of the oil and you make the turn off and it drops to near zero and you only have a little oil left in reserve. I assume this is why they suggest setting the lower setting for the average Joe who may really need this sort of band aid for a poor oil system.
Gary I agree with everything you say...except that if the extended piston air pressure is 20 that the compressed air pressure would still be 20....physics don't work that way my friend.
Canton’s instructions say “7 to 10 PSI”, so why not follow the instructions?
I think what makes this confusing is air is compressible. Obviously, if the air were a solid liquid, not a compressible fluid, it would be easily intuitively understood that the volume occupied by air displaces oil.
The simplest way to understand this is: Air has mass. The more air you put in the cylinder, the less room there is for oil.
You can prove this to yourself if you charge the empty cylinder at various pressures and fill it with oil from the running engine, and then see how much oil you get out of it. The higher the static air pressure on the empty cylinder, the less liquid it will hold at operating pressure, 60-100 PSI-whatever. If it is OK with you for your engine to run out of oil reserve at 20 PSI then go for it, because the cylinder will be empty at 20 PSI if that was the empty charge pressure.
I think what makes this confusing is air is compressible. Obviously, if the air were a solid liquid, not a compressible fluid, it would be easily intuitively understood that the volume occupied by air displaces oil.
The simplest way to understand this is: Air has mass. The more air you put in the cylinder, the less room there is for oil.
You can prove this to yourself if you charge the empty cylinder at various pressures and fill it with oil from the running engine, and then see how much oil you get out of it. The higher the static air pressure on the empty cylinder, the less liquid it will hold at operating pressure, 60-100 PSI-whatever. If it is OK with you for your engine to run out of oil reserve at 20 PSI then go for it, because the cylinder will be empty at 20 PSI if that was the empty charge pressure.
Joined
·
3,615 Posts
I run 7 psi of preload in my Accusump (per the instructions)..
It's clear to me that the higher your preload pressure, the less volume of oil the accumulator will hold..
Remember this... The pressure readings of the accumulator are NOT oil pressure readings.. But air pressure readings on the opposite side of the piston that has oil pressure..
The initial 7 psi of pre-load air pressure (with the accumulator internal piston all the way to the end).. That initial air pressure is compressed until it's pressure equals the running engines oil pressure..
Adding more initial air pressure does not push the oil out any faster than if you ran 1 psi of initial pressure..
The factory recommended 7 psi of initial pressure is probably the lowest figure they found that would fully inflate the accumulators internal bladder..
It's clear to me that the higher your preload pressure, the less volume of oil the accumulator will hold..
Remember this... The pressure readings of the accumulator are NOT oil pressure readings.. But air pressure readings on the opposite side of the piston that has oil pressure..
The initial 7 psi of pre-load air pressure (with the accumulator internal piston all the way to the end).. That initial air pressure is compressed until it's pressure equals the running engines oil pressure..
Adding more initial air pressure does not push the oil out any faster than if you ran 1 psi of initial pressure..
The factory recommended 7 psi of initial pressure is probably the lowest figure they found that would fully inflate the accumulators internal bladder..
Joined
·
7,145 Posts
I think of it this way...and I may be wrong so feel free to say so if I am. I think regardless of how much pressure you have in the accumulator wether it be 5 or 20 psi when the engine starts and begins to fill the accumulator with oil the pressure that presssure moves the piston against the air pressure on the other side. As the piston moves farther in (as oil pressure increases) and begins compressing the air on the other side of the piston that air pressure (psi) increases. I believe the piston would come to a stop when the air pressure on one side matches the oil pressure on the other side. If for some reason you loose oil pressure the compressed air will reverse the piston expelling oil because the air pressure is now more than the oil pressure. Now I can see someone's point of running 20 psi as opposed to lower pressures. I would think if you are running 20 psi that the accumulator would not take as much oil (volume) because the air pressure on the other side will equallize faster with a lesser volume of oil. The only benefit of running 20 psi that I can think of is in the event that the engine looses oil pressure and the accumulator expells oil in the engine the lowest oil pressure being expelled would not be any lower than 20 psi until it's empty but this would come at the exspense of having a lesser volume of oil to expell. Make any sense??
That's the entire point right there. If at rest you have 20 psi in the non oil side of the piston, then running, you will still have equal pressure on both sides of the piston. The oil volume will be less of course. If the pump pressure suddenly goes to 0, you have all that oil volume that will take time to be pushed into the engine. The pressure it is being fed with in this case will never drop below 20 until the supply of oil in the accumulator is exhausted. If you have 5 psi statics behind the piston, then there is virtually no pressure to push the last amount of oil into the engine. The point is probably moot anyhow, since the amount of oil that gets to the engine with enough pressure to go where it needs isn't all that much different in either case. I do run about 8 psi behind my piston, but I never run out of oil in the accumulator, so I really don't think it would hurt to put a bit more pressure in there. I don't think it would help anything greatly either.
Joined
·
3,615 Posts
That makes sense... But with the lower pre-load pressure, when the pressure drops to 20 psi.. You may still have a half quart of oil flowing out..
In all honesty, it comes down to personal preferences.. I like 7 psi cause with 9 1/2 quarts of oil and my accumulator fully charged.. My engine oil level is where I like it..
The reason I put the accumulator on in the first place.. Is because I have an oil pressure warning light that comes on at 25 psi.. And when I popped the chute at the finish line.. It would flicker..
Joined
·
20,103 Posts
Bellman it makes no sense to run more than 7psi. All you need is enough pressure to keep the piston at the bottom of the accumulator when there is no oil pressure. Anything over that will result in loss of stored volume in the accumulator.
More pressure will not push the oil out of the accumulator faster. All it will do is defeat the purpose of the accumulator.
There is no such thing as the “more pressure” some of you think a higher empty pressure will provide. The only thing higher initial pressure gives you is less stored oil volume to be available when you need it.
When the engine is running, the pressure on both sides of the piston in the accumulator is exactly the same as the engine oil pressure.
Do you realize there are some less expensive accumulators that are just a slender cylinder, vertically mounted, which have no piston and no initial charge pressure? They just have the trapped air above the liquid level.
When the engine is running, the pressure on both sides of the piston in the accumulator is exactly the same as the engine oil pressure.
Do you realize there are some less expensive accumulators that are just a slender cylinder, vertically mounted, which have no piston and no initial charge pressure? They just have the trapped air above the liquid level.
Joined
·
7,145 Posts
I bought a CVR just last week and here recently finished the install. I am waiting on the carb to get back as of now. In the meantime my accumulator did not come with instructions. After calling they advised only 5 psi. I think thats a little low. I will probably end up running between 8 and 10. If I can have at least 10 psi when the accumulator empties I think that will be more than enough. One thing I did learn by reading all this is that when I drive on the street I need to keep the valve closed cause I never though about the constant movement of the piston back and forth from oil pressure fluctuations. All that movement can't be good for wear purposes. I think I will just put it on a single toggle and only use it as a prelube on start ups but on full passes at the track it will stay open.
Joined
·
1,767 Posts
Yeti
I'll try not to confuse myself anymore then I am. Someone smarter then me tried to get me on board with your views and I was almost a Yeti master beleiver. Until my hamster started turned again
If my motor was sitting at 60psi, with the accumalator full with 6psi behind the piston, ( gauge on accumalor also reads 60psi) and instantly (magically) removed the oil pump drive what pressure would be logged at the back side of the accumalator say like .5 of a second, and then 1 second and 2 seconds after the oil pump drive was removed ?
This answer will help me wrap my head around a few things
Thanks for the discussion
I'll try not to confuse myself anymore then I am. Someone smarter then me tried to get me on board with your views and I was almost a Yeti master beleiver. Until my hamster started turned again
If my motor was sitting at 60psi, with the accumalator full with 6psi behind the piston, ( gauge on accumalor also reads 60psi) and instantly (magically) removed the oil pump drive what pressure would be logged at the back side of the accumalator say like .5 of a second, and then 1 second and 2 seconds after the oil pump drive was removed ?
This answer will help me wrap my head around a few things
Thanks for the discussion
You got me to blow the dust of the HP48. After this you can calculate this stuff yourselves.
I don’t understand how anyone can think the people who manufacture accumulators don’t know how to use them or are purposely giving you bad advice when they say to use 5 PSI (approx) charge pressure.
Assuming the volume of the Accusump is 3 qt. and initial temperature is 80°F and assuming 1.4 polytropic constant (the ratio of specific heats for air Cp/Cv).
3 qt. is approx. .1 cu.ft.
Initial volume = .1 cu.ft. on air side of piston, 0 cu. ft. oil
5 psi. initial air pressure
60 psi. = .0169 cu.ft. on air side of piston = 0.0831 on oil side = 2.43 qt oil volume
20 psi. initial pressure
60 psi. = .0456 cu. ft on air side of piston = 0.0544 on oil side = 1.63 qt. oil volume
So …….. If you start with 5 psi. you will store 2.43 qt. oil in the Accusump.
And …… If you start with 20 psi. you will only store 1.63 qt. oil in the Accusump.
You can daydream and confuse yourself about all the other what ifs, this and that’s or whatever’s, but the stored volume of oil is increased by 50% if you use 5 psi. instead of 20 psi.
And again ….. if you use 20 psi. the tank is empty at 20 psi.
If you start with 5 psi. then at 20 psi. the tank still has 1.1 qt. left to supply the engine.
An engine has a much greater need for oil when the pressure drops below 20 psi.
I don’t understand how anyone can think the people who manufacture accumulators don’t know how to use them or are purposely giving you bad advice when they say to use 5 PSI (approx) charge pressure.
Assuming the volume of the Accusump is 3 qt. and initial temperature is 80°F and assuming 1.4 polytropic constant (the ratio of specific heats for air Cp/Cv).
3 qt. is approx. .1 cu.ft.
Initial volume = .1 cu.ft. on air side of piston, 0 cu. ft. oil
5 psi. initial air pressure
60 psi. = .0169 cu.ft. on air side of piston = 0.0831 on oil side = 2.43 qt oil volume
20 psi. initial pressure
60 psi. = .0456 cu. ft on air side of piston = 0.0544 on oil side = 1.63 qt. oil volume
So …….. If you start with 5 psi. you will store 2.43 qt. oil in the Accusump.
And …… If you start with 20 psi. you will only store 1.63 qt. oil in the Accusump.
You can daydream and confuse yourself about all the other what ifs, this and that’s or whatever’s, but the stored volume of oil is increased by 50% if you use 5 psi. instead of 20 psi.
And again ….. if you use 20 psi. the tank is empty at 20 psi.
If you start with 5 psi. then at 20 psi. the tank still has 1.1 qt. left to supply the engine.
An engine has a much greater need for oil when the pressure drops below 20 psi.
Joined
·
7,145 Posts
I finally got mine going Saturday afternoon. I filled the accumulator with 20 psi and opened the valve (electric) to make sure all the oil was out then bled it down back to 10 psi. When I started the motor I noticed that it did take away some of the oil pressure but just for only about 10 seconds. I figured that the valve really only holds pressure one way and will let oil pressure in even when closed. As soon as I opened the valve on the next start up the pressure bounced back up I guess due to the fact the oil pressure is being held up higher by the accumulator. So after letting the engine fill the accumulator I shut it down and then open the valve and see just how long it will take to empty. By watching the gauge and listening you can see and hear when the accumulator is empty. Mine made a bubbling noise as it emptied. It took about 37 seconds to empty. So now I put 20 psi in and do the same. Since my gauge has a 20 psi mark it will be easier to read. I open the valve and its empty in about 17 seconds. Not a scientific test by any means....lol. Also after letting it sit over night I lost all the pressure in the accumulator. Oh well....gotta figure that one out now.
If you follow the instructions and run the piston to the bottom and then bleed the pressure back to 6psi then start the car what does the gauge on the accumulator read when you start the car? Does the pressure rise due to the compressing of the volume of air?
Joined
·
3,066 Posts
Right here. We also use nitrogen instead of compressed air to avoid pressure changes with big swings in temperature.
Joined
·
7,145 Posts
Yes I did that except I used 10 psi instead of 6. When I shut the engine off the accumulator gauge reads the highest oil pressure it has seen during that cycle. When I shut the engine off it eventually looses pressure. I know it's not the valve cause it would loose pressure before I put it in the car. I called CVR and they said that was normal but now I think not. Gonna give them a call today. If they can't send me another I will probably end up with a Moroso which is probably what I should have done in the first place.
You’ve proven it takes longer to empty the larger amount of oil you have when you start with less initial pressure than it takes to empty the smaller amount of oil you have when you start with more initial pressure. Who would have thought?
The pressure reads exactly the same as the engine oil pressure. If it doesn’t, one (or both) of the two gauges is inaccurate.
So if you have it with an electric shutoff it should hold and show the oil pressure that the engine had when you shut it off, correct? Looked at a friend's car with a Canton accumulator and the gauge was at zero. I'll have to look at it again.
If you have an accumulator and change the oil I'm guessing you just open it and all of the oil will flow into the motor so you can change all of it. Then when you start the engine you have to top it off the amount the accumulator holds.
If you have an accumulator and change the oil I'm guessing you just open it and all of the oil will flow into the motor so you can change all of it. Then when you start the engine you have to top it off the amount the accumulator holds.
41 - 59 of 59 Posts
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
