Hoping to not open a can of worms but what is the opinion on suction strainers on mobile machines. My skid steer came with a suction strainer for the charge pump and a separate suction strainer for the gear pump. Never had a problem in this regard but a lot of equipment has done away with suction strainers because they don't do much and can lead to cavitation. Curious what others think?
I dont use them...when it is cold outside there is no bypass
The suction strainer is your last line of defense for your pumps. I can't imagine a good reason to take them out. Rondig had mentioned Cold weather start up. If that's the case why not just run a lower viscosity oil? You're right about a year ago there was a serious debate about whether or not the use of a suction strainer was prudent. My position is if the manufacturer decided it was useful then it should be there because they are not in the habit of spending money on something that they don't have to do Good luck
I think you will be looking hard to find a mass produced machine that doesnt have some kind of screen/filter before the charge pump, or right after it.... There won't a loop direct to tank..... Not so long as oil buckets with dirt in the bottom
Screen before the pump - to stop the pump crapping itself as a result of whatever might be sucked from the tank. Screen after the pump - to stop shrapnel from a pump failure contaminating the whole system. First one needs servicing every time the hydraulic oil is changed, second one only needs servicing in case of a mechanical hernia in the pump. Agree 100% with fwf & mb that if there are suction/cavitation issues in cold weather with a suction screen in the system then the oil is too high a viscosity.
Thanks for the replies. A couple of sites online make it out that suction filters will destroy your hydraulics.
They meant NOT having one will destroy your system. Probably a simple auto-correction!?
Are you kidding? If you have seen the junk I have seen stuck to suction screens... you would never ask that question.
Here's a couple. Some people on this forum take the 1st guy as being the gospel on hydraulics. http://www.insanehydraulics.com/letstalk/suction.html https://www.hydraulicspneumatics.com/blog/truth-about-hydraulic-suction-strainers
I respectfully disagree with the positions stated. I stand by my earlier position. A manufacturer is not, NOT, no way in hell, going to spend one nickel on anything deemed unnecessary. Excavators have sump strainers. Loaders usually have return filter well with standpipes in the tank to not draw the trash off the bottom. Pavers, rollers, grinders screened inlet manifolds inside the hydraulic tank. That's a lot of unneeded expenditure that those shareholders are gonna want back, ya think? I'm typing here, albeit slowly, I can see how it mind sound snippy, it's not meant that way. If your equipment pump $h!ts the bed, after it hurts your function, what stops it from hurting your travel pump? If your travel motor craps out and spews trash out case drain port, what protects the rest of your system, the strainer. Everyone thinks that filters are 100% efficient. If you look at your schematics, usually only half or 3/4ths of the oil pumped is filtered on the way back. Some sneaks back in case drain, which may or may not be filtered, some gets by filter in bypass mode. Murphy is everywhere, waiting for us to slip up. You don't have to invite him over for breakfast.
This image is a sump strainer I serviced Wednesday. That sludge is all kinds of evil. Bits of steel, piston packing, bits of back up ring, slivers. All things bad for an excavator. The screen was there to stop it. That could have been laying waste to the entire system.
Hey!! Wait!! The internet don’t lie.
You're right, the internet doesn't lie, it's the muhfuggers who post on it, spreading disinformation and shenanigans.
And for a bit of lightening up
Thanks for that. I think the OEM's would specify suction strainers with much higher flow rates than what the machine actually has so there is no chance of cavitation. One of the arguments I read is that suction strainers were installed because that was standard practice back in the day and they don't want to break tradition. Here's another one saying not to use them. https://www.mobilehydraulictips.com/7-ways-avoid-cavitation/
I read those articles with a growing feeling of incredulity, as in "You what..?" or more like "You ******* what ..?" I think that there has to be a differentiation made between machine hydraulic systems and industrial hydraulic systems in regard to the environment in which they operate. Also one statement made me (kinda) laugh, quote "Don’t get me wrong, it could take an easy decade to clog a suction filter, but when it does clog, ........" My response - well service the ***king thing as per the manufacturer's recomendations then, which is every time the oil is changed, usually one year or 2000 hours intervals. That way your suction strainer will never reach the decade it needs to clog. FFS can I have some of whatever these clowns are smoking..?
Still have the OE Strainers on my Antique Allis, know why they are there and could have cut them out but ARE cleanable and a NECESSITY especially on OLD ABUSED machines. One Dope/Dumbazz gets his hands on a machine and red glues ALL the gaskets back in place instead of buying new or fabri-cobbling replacements or just using it to compensate for lack of skill and you WILL understand the necessity of strainers.
Worked on many an Allison 5-6,000 series with convertor housing scavenge screens plugged solid with silicone drippings from people that don't believe in new gaskets.
Most mobile equipment has a pressurized system just for cavitation control. I've set many a Wabco scraper up to be pressurized by the air brake system with a regulator and check valve to boost the steering system. It made a huge difference in steering response and lack of cavitation pitting in the valve block on the pump. Waiting for the system to pressurize from heat took far too long. And all those machines had the suction screens serviced on a regular basis.
I try to use 518 wherever I can in place of silicone. It doesn't glob up to plug orifice and passageways like sillycone does. I've seen many problems, cooling systems, lube systems, hydraulics, even had a power divider crap the bed from too much sealant.
I think the big link-belts were like that. Had a dedicated compressor just to pressurize the hydraulic tank. Pretty simple and efficient.
Drain and remove a hydraulic tank from a skid steer with 3,000 hours on it and tell me you're ok with all that crap being sucked straight into the charge pump. Skid steers are the worst IMO since there are usually no return filters, so any debris and wear material is going to build up on the bottom of the tank. I agree with the above. If it wasn't needed, the mfg would not waste money developing/installing it.
I cut the hyd. return line filter open and didn't find anything unusual or visible metal filings in it but I change the hyd. filter every 2nd engine oil change. Used to do it every oil change but that was too much IMHO. Could a suction strainer be back flushed to clean any debris out of it and then just empty out of the reservoir? Reason I ask is because getting the suction strainer out would be a major headache. Would almost have to take the engine radiator out and then remove some hyd. pipe fittings to have enough access to get at the cover plate and then the strainer. A Tee pipe fitting connects to the charge pump strainer. One side comes from the oil cooler and the other side feeds the charge pump. This might help prevent cavitation too since oil isn't just being pulled up from the tank. The line from the oil cooler is after the oil has gone through the filter so some oil to the charge pump is filtered and some goes through the strainer. I don't think the lines to the T would be too hard to remove and I could raise them both up above the T and pour some varsol or other solvent down them that would go straight to the strainer and into the bottom of reservoir which has a magnetic drain plug. Could blow some air down them too. Since the tank is already drained I thought it could at least give me an idea how bad the strainer might be and if I should go to the trouble of getting it out. No sludge or milky oil came out of the reservoir. Good news is I had some help and got the new Hyd. motor put in and got the slotted nut that holds the sprocket on tightened enough to get the cotter pin in. Called for 350 ft./lbs. and I think we're a little tighter than that but what can do when have to install a cotter pin. LoL Going to rent a filter cart for the new oil and run the oil through it a couple times to make sure everything is cleaned out. Ran machine for less than 7 hours when noticed hyd. oil was low and no leaks on the ground. Only place it could be was in the chain case which was about 3 gallons overfull.
Here's a good article on suction strainers. http://www.flowezyfilters.com/pdfs/keeping_the_lines_clean.pdf
A very good read, kinda sums up what we've been saying. Good luck, good night.
Do you wanta share some of it????
You’d have to put it in the mail, and where I live people get locked up for doing that ..... thanks I’ll pass.
The thread is full of circular logic. The people who make filters and strainers say you have to have them while others say they are not necessary if you keep the oil clean. The last linked article was written by someone who sells filters. The article published by the "expert" says you don't need them, they only reveal "lazy" people who don't do their maintenance. Both arguments are correct on the face of them. I do think it's funny that the filter seller didn't know the pressures common today on high pressure systems and then put in the statement concerning "bypass" on a suction strainer. My take is that there are components in any hydraulic system that fail prematurely. Drive motors have case drains that send oil directly back to the reservoir. Debris from a failure usually takes that path to the tank and to the suction of the pump. So if a motor fails at 1,000 hours and the usual pump life is 5,000 hours or more, do want to have to replace the pump at 1,000 hours? Say a cylinder rod gets bent by some unforeseeable outside force and starts shaving a thousand little knives off the inside of the barrel with each stoke, would you not want a suction strainer? Some will say the cylinder returns go through the cooler and then to the return filter. But truth is when the oil is cold the bypass on the filter drops oil directly into the tank. The same goes when the filter gets plugged with debris. Suction strainers are sized by the manufacturers taking into account the operational characteristics the system is intended to run in. When I think of it now, I'm picturing it like a fire extinguisher. Fires aren't supposed to happen but they do. Components in a hydraulic system aren't supposed to fail but they do. How frustrating do you think you would feel being at a fire without something to fight it with? What would you think about a broken swing motor in an excavator taking out every component in the system?