Steering Reservoir Tech (and Demo)

[ScottRS]

How is the pump going to cavitate if all air has been removed from solution in the oil? I'm not really suggesting running the system under a constant vacuum though. If there's a 10psi pressure relief and the oil heats up with use/expands, it could possibly pressurize the air in the top of the reservoir up to 10psi in this case. Without a vacume break/relief, it's possible that a vacuum will occur when the oil cools and the vehicle is sitting. Is the air in solution not being pulled from the oil the entire time the vehicle is sitting and gathering at the top of the reservoir? How is that a bad thing? I don't think it would take very long for the oil to heat up/expand enough after starting the engine to relieve whatever vacuum existed while at rest(IE reach 0psi or 14.5/atmospheric).In fact, it's not even a given that a vacuum would ever form if the pressure never exceeded 10psi.

The vacuum to bleed bit isn't a bad idea, probably a good one honestly. Just a pain to implement.

Cavitation is the instantaneous, localized, low pressure area forming in a vacuum in which the fluid boils due to the very low pressure, I think HD explained it better than I could. It boils the fluid in that low-pressure area, forming a bubble of vapor, when the low pressure area goes away, the bubble of vapor collapses back on itself, impacting everything nearby. That impact pounds the metal pump vane or whatever and erodes it. You can have cavitation at ridiculous pressure; a submarine prop can cavitate hundreds of feet below sea level if spun fast enough because the viscosity of the water is such that it can't flow fast enough into the space just-vacated by the prop blade. System pressure/vacuum is just the starting point. This is also why high pressure and flow fuel pumps don't do well without a lift pump, they're trying to pull too much vacuum on the inlet side, if you add a lift pump, you spread the work and reduce the degree to which one pump is pulling a lot of vacuum at one point, reducing the tendency to cavitate at any one location.

 

[DesertCJ]

"Vaporous cavitation is an ebullition process that takes place if the bubble grows explosively in an unbounded manner as liquid rapidly changes into vapor. This situation occurs when the pressure level goes below the vapor pressure of the liquid.

Gaseous cavitation is a diffusion process that occurs whenever the pressure falls below the saturation pressure of the noncondensable gas dissolved in the liquid. While vaporous cavitation is extremely rapid, occurring in microseconds, gaseous cavitation is much slower; the time it takes depends upon the degree of convection (fluid circulation) present."

From https://www.machinerylubrication.com...wear-hydraulic

OK, I knew what I was thinking but couldn't explain it. A slight vacume with the vehicle off would pull the saturated air out of the oil. When the oil heats and expands to create pressure, the pressure would prevent vaporous cavitation. Now, would the vacume be enough to initiate vapor cavitation right off the bat when the engine fires up? That's the remaining question in my mind. Not even sure why I'm stuck on this, I don't have any steering issues...lol.

Edit: The bubbles shown being separated from the water in the clear reservoir in the beginning of this thread would have to be saturated air which would also be removed under a vacume...

 

[Provience]

Edit: The bubbles shown being separated from the water in the clear reservoir in the beginning of this thread would have to be saturated air which would also be removed under a vacume...

yes, the difficult part is knowing exactly when air get's reintroduced. the vortex and screens are passive, a constant vacuum or even a vacuum at idle would be adding work and a vacuum that is operator controlled would require some clear reference section that the operator could see and react to, or some other not as easy method of monitoring.

 

[RadialDynamics]

Yes, in a sense we are talking a double edged sword where a pressurized reservoir will push more air into solution but will also reduce the likelihood of vapor bubbles forming in the pump or feed line as shown in my pressurized reservoir demo. Partial vacuum in the reservoir will cause the pump to cavitate severely which we want to avoid at all costs because vapor bubbles in hydraulic fluid, whether from air coming out of solution or oil vapor, will not only implode and erode pump internals, as noted, but will also generate heat, break down the oil, be a poor lubricator between metal components in the pump, and will degrade steering feel due to compressibility of the vapor bubbles.

Also think about this, if the reservoir had a 10 PSI relief valve with no anti-vacuum valve and therefore created vacuum in the res as fluid cools and contracts, sure you might pull some air out of solution, but that air is now in a closed/sealed space so aside from the severe cavitation that you will get next time you start your vehicle, as the fluid expands you will be pressurizing that same volume of air again which will be just as likely to re-introduce dissolved air into the fluid.

I continually come back to the concept of keep it simple, minimize cavitation and chances to introduce new air, and use a reservoir that can remove vapor bubbles as they occur.

 

[DesertCJ]

OK, so any vacume while the pump is spinning is very bad. Also, pressure in the reservoir might be causing as much of a problem as its solving? I don't really understand how pressurizing the reservoir is going to dissolve air into the oil but honestly I'm kinda just thinking I'm not going to fix something that isn't broken.

 

[RadialDynamics]

OK, so any vacume while the pump is spinning is very bad. Also, pressure in the reservoir might be causing as much of a problem as its solving? I don't really understand how pressurizing the reservoir is going to dissolve air into the oil but honestly I'm kinda just thinking I'm not going to fix something that isn't broken.

Yes, vacuum is bad due to the cavitation that it causes and in my experience, without question, the benefit of reduced cavitation from a pressurized reservoir far outweighs the slight increase in dissolved air content that could occur as a result of that increased air pressure.

 

[PAE]

This sphere has the pickup shown with a stainless an fitting attached but does not extend into the center and has baffles matrix inside to keep the fluid from moving as much as without a baffle.

Super cool!
Round aviation reservoirs usually have a pickup tube going to the center of the sphere. Regardless of orientation the air will always be opposite of the side of gravity or centrifugal force and the pickup tube will be in the middle which is the furthest distance from the sides.
My first reservoir on the buggy used this concept in tube form to keep the air at the ends of the reservoir tubes when the buggy was on its side. That was back when I had full system flow going through the reservoir. While it worked great I learned that a reservoir of that size was not needed if the system could be supercharged or recirculated or whatever you want to call not sending full flow through the reservoir. That when the reservoir size dropped from 18 gallons to 1 gallon.

 

[welndmn]

Kinda related, how is the new trend with a pressurized reservoir?
I have an old HOWE reservoir on a trail only rig, is it worth it to weld on a radiator cap end?
No real issues with anything besides spilling fluid out the vent when it rolls over.

 

[ScottRS]

OK, so any vacume while the pump is spinning is very bad. Also, pressure in the reservoir might be causing as much of a problem as its solving? I don't really understand how pressurizing the reservoir is going to dissolve air into the oil but honestly I'm kinda just thinking I'm not going to fix something that isn't broken.

I don't think (some) pressure in the reservoir is a bad thing. Lots, is, not because of the fluid dynamics but because it blows seals out of PS pumps. If we had pumps that could deal with it, precharging systems would be a very good thing.

This comes back around to my thoughts on a surge tank. You will get bubbles. That's life. How you separate them and keep them away from the pump inlet, is critical. This is where floating pistons come into play, or a surge tank with fluid in it is essentially a redneck permeable floating piston. Bubbles will come out, but can't be drawn back in. Where it looks to me like RD has something really cool going on, is he's managed to integrate a surge tank into the primary reservoir and not separate like I have. I haven't yet figured out a workable way to do that within the package confines that I need.

 

[DesertCJ]

So here's another question. Presumably, one half of the pump is seeing somewhere between 1000psi-1600psi on the outlet side? But 20psi on the inlet side is blowing seals? What am I missing here?

 

[Im4yotas]

Aircraft pumps use pressurized reservoirs to ensure enough head pressure to feed the pump at high altitudes when atmospheric pressure is too low. Might be worth looking into.

 

[mobil1syn]

So here's another question. Presumably, one half of the pump is seeing somewhere between 1000psi-1600psi on the outlet side? But 20psi on the inlet side is blowing seals? What am I missing here?

input shaft seal is on the low pressure side

 

[DesertCJ]

Where would this seal be?

Is this description wrong on the pics? Looks like the seal around the shaft on the front of the pump is open to the high pressure side?

 

[ScottRS]

Where would this seal be?

Is this description wrong on the pics? Looks like the seal around the shaft on the front of the pump is open to the high pressure side?

Right behind the pulley. It's not a high pressure seal. More like a tiny little pinion or front main seal.

 

[DesertCJ]

I only see what looks like a snap ring and a shielded bearing behind the pulley on a TC pump. I'm assuming that their must be some type of seal behind the bearing...

 

[AgitatedPancake]

Depending on pump type, on TC's behind that sealed bearing is a seal. Right at the back side of the seal is a small diameter orofice that leads back up to the intake side of the pump. CB's have a bushing instead of a bearing, but the same passage still exists right behind the main seal. So as I understand it, a small amount of fluid bleeds from the high pressure side to the back of the seal, where it's released back into the reservoir. So it's an intentional bleed condition to circulate fluid through the seal area without allowing it to build more pressure than is in the reservoir. But as you increase reservoir pressure, you increase the PSI differential on that low PSI seal

 

[DesertCJ]

Depending on pump type, on TC's behind that sealed bearing is a seal. Right at the back side of the seal is a small diameter orofice that leads back up to the intake side of the pump. CB's have a bushing instead of a bearing, but the same passage still exists right behind the main seal. So as I understand it, a small amount of fluid bleeds from the high pressure side to the back of the seal, where it's released back into the reservoir. So it's an intentional bleed condition to circulate fluid through the seal area without allowing it to build more pressure than is in the reservoir. But as you increase reservoir pressure, you increase the PSI differential on that low PSI seal

That's the money shot! So there's a bleed hole from high pressure side of pump back to low pressure inlet side. If fluid is flowing like that, then by definition it has higher pressure than the reservoir. Increasing the pressure in the reservoir by charging with air or nitrogen is going to decrease the psi differential not increase it. That bleed port may be there just to circulate fluid and lube the seal? That seal is definitely not getting pushed out by 20psi in the reservoir though. Oil might get pushed past it, but the seal is not blowing out from behind the bearing.

 

[AgitatedPancake]

That's the money shot! So there's a bleed hole from high pressure side of pump back to low pressure inlet side. If fluid is flowing like that, then by definition it has higher pressure than the reservoir. Increasing the pressure in the reservoir by charging with air or nitrogen is going to decrease the psi differential not increase it. That bleed port may be there just to circulate fluid and lube the seal? That seal is definitely not getting pushed out by 20psi in the reservoir though. Oil might get pushed past it, but the seal is not blowing out from behind the bearing.

The restriction is in the bleed path it takes to get to this point, where it can flow unrestricted back into the reservoir. So this area at the back of the seal is a low pressure zone where the pressure matches reservoir pressure. So the pressure differential is outside (atmospheric) pressure versus the internal pressure in the reservoir. So atmospheric pressure stays the same while reservoir pressure increases will create force trying to push out/past the seal. TC pumps are somewhat contained by the sealed roller bearing retained by a snap ring which may or may not mean they can handle a higher pressure differential, but the seal on CB pumps and others isn't retained by anything other than the stamped sheetmetal seal housing press fit.

 

[RadialDynamics]

The restriction is in the bleed path it takes to get to this point, where it can flow unrestricted back into the reservoir. So this area at the back of the seal is a low pressure zone where the pressure matches reservoir pressure. So the pressure differential is outside (atmospheric) pressure versus the internal pressure in the reservoir. So atmospheric pressure stays the same while reservoir pressure increases will create force trying to push out/past the seal. TC pumps are somewhat contained by the sealed roller bearing retained by a snap ring which may or may not mean they can handle a higher pressure differential, but the seal on CB pumps and others isn't retained by anything other than the stamped sheetmetal seal housing press fit.

All of this. Plus one more note, just because the seal is retained behind a ball bearing in the TC pump, it may not push out 100% but can still push out enough to leak. Also even if you were to get lucky enough not to damage the seal, the higher the internal pressure behind the seal (reservoir pressure), the more the seal lip grips onto the pump shaft leading to higher friction/heat/wear on the seal lip.

 

[ParadisePWoffrd]

What about using an accumulator, like used with engine oil? You might still need to have a small reservoir to manage the multiple inlets and outlets, but maybe it could be sealed with an accumulator feeding it also?

 

[Provience]

What about using an accumulator, like used with engine oil? You might still need to have a small reservoir to manage the multiple inlets and outlets, but maybe it could be sealed with an accumulator feeding it also?

cost is high, packaging is painful

 

[Bebop]

What about using an accumulator, like used with engine oil? You might still need to have a small reservoir to manage the multiple inlets and outlets, but maybe it could be sealed with an accumulator feeding it also?

How would you bleed that ?

 

[HYDRODYNAMIC]

How would you bleed that ?

I had been thinking about this for awhile now.
The accumulator does not need to hold air, only liquid. Install the accumulator vertical with port up. No air will enter the accumulator but it will still flow oil in and out. If air bubbles entered for a moment, they would flow right back out.
Install an air trap at the highest point were bubbles can work their way up and be caught and purged out. Really any sealed reservoir would work for this as long as it had a vent on the top to purge air and bubbles. The reservoir would operate 99% full of oil, 1% being air that would need to be purged next time that you didn't get the first time.
The accumulator could possibly be a large bore air cylinder with a rod to identify where the piston is for filling purposes. To fill, you would pump the fluid in through a QD port somewhere on the system. I used one of the small bucket pumps for my VVR sealed reservoir and it worked great. The size of the cylinder could be near the same as a reservoir, 4" diameter x 6" stroke. I am also thinking that a compression coil spring around the rod either inside or outside would be better than an air charge. If it was outside you could add some all thread to extend the spring working distance to prevent coil bind. The spring will keep a more linear force on the liquid. An air pocket would be too small to keep a min max of 10 PSI on the system with temp change and potential leaks. If you wanted to get fancy you could run without a spring and use a 10psi air regulator from an on board air system to keep an exact force on the piston.
I could see myself doing this at some point in time when I have more time. It would be a really easy retrofit by simply adding a T for the accumulator. The Radial Dynamics, Howe, PSC reservoirs are already sealed. Surplus air cylinders are plentiful and cheap. I don't see any real special skills or tools to pull it off either.

 

[ParadisePWoffrd]

How would you bleed that ?

How do you bleed it with an oil system?

My thoughts are teeing it into the pump feed line, similar to how you would an oil pan, to provide more fluid when the system can keep up, to help prevent pump starve or cavitation. The pressures are so low there though, not sure how it would refill.

Maybe teeing it into the pump outlet would help out in those instances where the load in more than the pump could handle? Not sure a typical accumulator would handle those pressures, but maybe something like HYDRODYNAMIC was mentioning, might.

 

[Bebop]

How do you bleed it with an oil system?

My thoughts are teeing it into the pump feed line, similar to how you would an oil pan, to provide more fluid when the system can keep up, to help prevent pump starve or cavitation. The pressures are so low there though, not sure how it would refill.

Maybe teeing it into the pump outlet would help out in those instances where the load in more than the pump could handle? Not sure a typical accumulator would handle those pressures, but maybe something like HYDRODYNAMIC was mentioning, might.

I misunderstood you. I thought you wanted to install an accumulator on the reservoir side, with a sealed reservoir.
If you want to add it on the pressure side, there is almost no bleeding to do, except the line on fill up, which isn't super hard to do.

As you said, the main problem will be system pressure as a standard accusump works around 60 psi vs the 1500+ psi of a hydraulic system. Most feasible solution would be to turn a hydraulic cylinder into an accumulator.

Now if you want to add it on the feed line between the reservoir and the pump inlet, since there is a vaccum on this line, IDK how you would fill the accumulator up in the first place.

 

[Im4yotas]

High pressure hydraulic accumulators are very common in the industrial world. I'm not convinced they would make any difference in our application unless you had a really big one, which is more trouble and money than its worth.

Someone feel free to prove me wrong, though!

 

[Bebop]

High pressure hydraulic accumulators are very common in the industrial world. I'm not convinced they would make any difference in our application unless you had a really big one, which is more trouble and money than its worth.

Someone feel free to prove me wrong, though!

They would also require a reservoir setup that could take the extra volume when the pump is off or not making any pressure, right ?

 

[Im4yotas]

They would also require a reservoir setup that could take the extra volume when the pump is off or not making any pressure, right ?

No, it works just like the accusump, or a shock remote reservoir.

 

[Bebop]

No, it works just like the accusump, or a shock remote reservoir.

The accusump empties itself in the oil pan (reservoir) when the engine oil pump isn't putting any pressure in the system. Unless you have a valve that's commanded with the ignition.

 

[Im4yotas]

The accusump empties itself in the oil pan (reservoir) when the engine oil pump isn't putting any pressure in the system. Unless you have a valve that's commanded with the ignition.

Ok, I think I understand your question now. Yes, your reservoir needs to have the extra capacity for the accumulator to dump into after you turn the engine off. And you definitely want to add the plumbing and switch to automatically drain the accumulator upon engine shutoff. Otherwise it will keep the system pressurized, which can be dangerous (see high pressure fluid injection injury).