You need a "T" because right now the oil goes from the pump to the engine. You use a "T" to add in the accumulator. It is not "inline" between the pump and engine.
Accusump shows a checkvalve in their installation instructions. This is why I thought it would be a good idea to have one. Apparently it seems like I don't.
Thanks Again everybody!
Rob
In reply to wvumtnbkr:
The oil pushes from an oil gallery( thats where the oil pressure sender is usually screwed into) into the accumulator. Not directly from the oil pump, so when you have low oil pressure it simply returns the pressurized oil back into the oil galleys and into the bearings. The oil will find it easier to exit the bearings as opposed to the pump.
The check valve that is mentioned in the post before last is actually so that oil goes towards the engine side of the t-intersection, not the oil cooler/filter side of the t-intersection.
Sounds to me like you are looking for an expansion tank similar to the ones used on heating systems, well tanks, and water supply systems that use a check valve. I suggest one of those small beige units designed for water supply. It is called a extrol 15 and is about half the size of the grey ones most people have hanging from their hydronic heating systems. It is constructed so that there is a rubber bladder in the middle. As you fill it with pressurized water, the pillow of air on one side of the bladder compresses. The bladder prevents the air from dispersing into the water over time. There should be a shraeder valve on the air side and a 1/2" male thread on the water side. Screw on an IPS ball valve and go from there. Total cost will be less than $35. Here is a link with specs. You can buy them at any plumbing supply.
http://www.pexsupply.com/Amtrol-101-1-15-Extrol-Expansion-Tank-2-Gallon-Volume-2556000-p
I strongly suspect the bladder in a plumbing expansion tank will not be compatible with engine oil.
wvumtnbkr wrote: Why do some of the accumulators have the internal piston? I figured that if you don't seperate the air and the oil that the oil would get "frothy".
Follow up question to this- what in an accusump would cause the oil to be frothy? There's nothing in there to stir things up.
Especially compared to the oil that is actually in the sump, which is exposed to air over the entire surface area of the oil.
I don't see how a piston would make it better or worse- since there doesn't seem to be a mechanism in the accumulator set up that would put air into the oil.
The piston in an Acuusump separates the oil side from the air side if you don't have the piston all you have is a tank full of oil it will do nothing to prevent the oil system from failing in a hard corner. Some cheaper units use a rubber bladder this is so they can use off the shelf tubbing and not have to machine the ID for the o-ring on the piston to seal. Both work as well as the other and should not foam the oil. The foam is normally from the oil pump caveatting when the pick up doesn't have enough oil around it it will suck some air. The pump compresses the air in to the oil as frothy foam the dip in outlet pressure makes the stored oil move out of the acuusump and in to the motor until one of two things happen the pump catches back up thus starts to refill the sump or the sump runs out of oil to push in.
Any hydraulic shop should have one at less cost on the shelf.
The advantage of keeping the air and water separate is flexibility of mounting. Without a piston or bladder, you have to mount the accumulator upright. With it, you can mount it in any orientation.
"I strongly suspect the bladder in a plumbing expansion tank will not be compatible with engine oil."
That is why many plumbing parts like this are stamped "WOG". That means water oil gas. And besides, it's going in a lemons car. Whether the rubber bladder lasts more than a few days is irrelevant.
tr8todd wrote: "I strongly suspect the bladder in a plumbing expansion tank will not be compatible with engine oil." That is why many plumbing parts like this are stamped "WOG". That means water oil gas. And besides, it's going in a lemons car. Whether the rubber bladder lasts more than a few days is irrelevant.
I have yet to see an plumbing expansion tank marked WOG. That marking appears on valves. I'm not sure the bladder would last an hour subjected to hot oil, and who knows what would happen if it failed. The rubber parts could easily find their way out of the accumulator into the engine. There are ways to save money when building a LeMons car. This ain't one of them.
Is this type of system totally absent from all OEM vehicles?
My Challenge car came with what looks like a home made Accusump. It's a 4" aluminum tube 15" long. One end has a welded cap, the other is an aluminum plate , held in place by a 4" C-clip. I haven't taken it apart, but I assume there's a piston inside. It was mounted horizontally. It doesn't look too hard to duplicate, aside from the piston. I'm also assuming there is some sort of seal(s) on the piston. If you can weld and have access to a lathe it should be something that you could DIY.
The piston keeps a constant quantity of air available. Mine came with 50psi, and after a season of stock car racing, it still does. Watching the oil pressure gauge in the Prelude ministock is scary without the Accusump. Long left turns = under 10psi without, 40 psi with. 55psi on the straight.
I don't see why a piston is required. Or a shrader valve for that matter. I think you need a check valve, a t fitting, a big hose, a ball valve and a big upright pipe.
There will be air trapped inside the pipe as the engine oil pressure comes up, and the air will pressurize to oil pressure. When the oil pump stops pumping, the air pressure in the canister will push oil out the bottom initially at engine psi, but then slowly falling as air volume decreases.
Oil pump output } check valve } t fitting - one side goes to where the oil pump output used to go, and the other goes to the ball valve and then the bottom of the pipe.
mr2peak wrote: Is this type of system totally absent from all OEM vehicles?
It's used on at least one of the LS variants in the Vette.
The only off the shelf item I can think of that's comparable would be a big Bimba double acting pneumatic cylinder, and those cost Accusump money.
This reminds me though, the other day I was wondering about the feasibility of using a single sub $100 industrial hydraulic gear pump as a scavenging pump for a cheap dry sump setup. Porsche got away with a single scav pump on the air cooled 911 and the VW racing guys get away with copying it, so the idea has some merit. That would give unlimited oil rather than hoping the accumulator outlasts the corner.
In reply to Robbie:
There is a limited amount of air available when its pressurised by the pump. With the piston, there is still 50 psi for all the flow.
mad_machine wrote: don;t some classic saab 900s also use hydraulic boosted brakes with a small electric pump to pressurise them?
My 91 does. There is a "bulb" with a bladder in it (accumulator) as well as an electric pump in the ABS system.
Streetwiseguy wrote: In reply to Robbie: There is a limited amount of air available when its pressurised by the pump. With the piston, there is still 50 psi for all the flow.
I don't understand what you mean. Even with a piston, the volume of the tank that the air takes up will change as oil flows in or out. If oil flows in, the volume left for air goes down and therefore the air will increase in pressure. If oil flows out, the volume for air increases and the pressure decreases.
I am still convinced that the piston's only benefit is that it makes it possible to mount in any configuration with respect to gravity. The piston keeps all the oil on the side of the sump with the oil hose. If you have no piston, you need gravity to do it for you, and therefore you need to mount the tube vertically and have the oil hose at the bottom.
In reply to Robbie:
The piston gives you some "preload", an empty tank with a hole/dip tube in the bottom that drains out (under pressure of the compressed air pocket) at shutdown/loss of pressure will quit forcing oil out with any appreciable pressures before it's empty. With the piston you can pump it up a little first so it's guaranteed to be shoving oil out to some degree (the preload pressure at minimum) until the piston hits the end of travel.
Robbie wrote: I don't understand what you mean. Even with a piston, the volume of the tank that the air takes up will change as oil flows in or out. If oil flows in, the volume left for air goes down and therefore the air will increase in pressure. If oil flows out, the volume for air increases and the pressure decreases. I am still convinced that the piston's only benefit is that it makes it possible to mount in any configuration with respect to gravity. The piston keeps all the oil on the side of the sump with the oil hose. If you have no piston, you need gravity to do it for you, and therefore you need to mount the tube vertically and have the oil hose at the bottom.
If you use a piston with restricted travel and a pre-pressurized, sealed air spring, then you can trade off total volume of oil for a slower pressure drop over that volume.
Imagine you have a cylinder with a total volume of 4 quarts. Without a piston it starts out with 4 quarts of 14.5 psi (absolute) air in it. Put in 50 psi (gauge, so 64.5 psi absolute) of oil and you end up with 3.12 quarts of oil and 0.88 quarts of air (*), both at 64.5 psi (absolute). Now let's say we need 2 quarts of oil supplied for emergency purposes, that will let the air expand to 2.88 quarts, dropping its pressure down to 20 psi (absolute) or only 5.5 psi (gauge). So you got 2 quarts out, but the pressure dropped a lot.
Now imagine the same cylinder with a piston in it that has a sealed air cavity behind it, but which is travel-restricted so that oil cannot take up more than half the cylinder. It starts out with the piston all the way at the bottom, and let's say we pressurize the air spring beforehand to 17.75 psi gauge (32.25 psi absolute). Put in that same 64.5 psi (absolute) of oil, and the piston will move to the fully retracted position, with 2 quarts each of oil and air, both at 64.5 psi (absolute). This cylinder can only deliver 2 quarts of emergency oil (vs the 3.1 that the no-piston cylinder can), but the lowest pressure you'll get in those 2 quarts is 17.75 psi (gauge), vs 5.5 psi from from no-piston cylinder.
(*) By the ideal gas law, PV=NRT, simplifying and pretending that the air temperature doesn't change as it gets pressurized. I'm also assuming that the cylinder takes up no volume in the second cylinder, or at least that the cylinder is enlarged so that you still have 4 quarts of usable volume in it.
In reply to codrus:
I agree, but it is the pre-pressurization of the air, not the piston, that gives you the extra oil pressure. You could put a shrader valve and pre pressurize the air with no piston too...
Once the engine is running and you have 50 psi air and oil in the tank, adding air with a pump will not further increase pressure, it will just drive oil out. This will increase the volume of pressurized air, which will give you the trade-off of less oil supplied but the final oil is supplied at a higher pressure.
In reply to Robbie:
But all your pressure would bleed off with the engine not running.
2002maniac wrote: In reply to Robbie: But all your pressure would bleed off with the engine not running.
Sure, but most air pressure will still bleed off even if you had a piston (with the exception that the piston would prevent you from pushing air into the oil system when the accusump empties). You would also put the entire accusump volume of oil into the pan.
That is why you need the ball valve at the outlet of the accusump. Open just before starting, close while idling before shutdown.
That all said, it does seem like an accusump could hurt the engine by increasing the amount of time it takes the engine oil pressure to come up when the engine is coming off idle. If idle psi is say 20, but high rpm pressure is 50, then the accusump will be at 20 psi with low oil volume at idle. When the RPMs come up, instead of high pressure oil going straight to the bearings, some of the initial pressure would go toward filling oil into the accusump and increasing the pressure in the sump, therefore reducing pressure and flow to the bearings. Seems like that would be bad.
Essentially the accusump is just damping the changes in oil pressure output from the pump. System pressure stays more constant as pressure drops at the expense of slower response when pressure increases.
The air behind the piston doesn't bleed off, you have a fixed number of air molecules in there set by pressurizing it slightly with no oil in it/piston fully extended. The ball valve is only necessary if you want to have the option of prelubing the engine at startup or would have some issue with the engine sitting around with several extra quarts in the pan.
You're right that it will slow the rise of oil flow (pressure is an indirect measurement, sufficient flow to keep them from gettign too hot is what we're after here) to the bearings some degree, but it seems people that use them find it to be a worthwhile compromise.
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