Help finding a hydraulic suction leak

[fast_st]

I have a pesky little problem, its a suction leak someplace on my log splitter. When its running I see bubbles coming from the return line, its a home made aluminum tank, 25 gallon with two baffles built in, solid on the top and a handful, maby 10-12 of 2 inch holes on the bottom to help strain out the air bubbles.

I thought it was the hydraulic pump, Haldex/northern tool 28 gpm dual stage. I have a 2" suction line that goes through a suction side filter/screen and necks down to a 1 inch line to go into the pump, I suspected the pump as one of the 4 bolts broke off sometime, found it while checking torque, and the pressed in intake fitting came loose as well.

I put in 4 new bolts, knurled and red loctited the suction line in place after giving the pump a good cleaning. Still showing air bubbles! Crap! tighten all the clamps and put the A/C vaccum pump on the tank vent and sucked her down to 10 inches. Well the tank drain had a little bubble leak, squirted gear oil on it and it was silenced, I applied oil to every joint and coupling, no change in the air bubbles percolating into the return line, tightened all clamps 1/4 turn more, no change. Pulled the pump off while still plumbed and applied oil around the shaft seal, no change in the rate of bubbling, one bloop every two or three seconds. I'd have to kick the vac pump on every five minutes to keep the numbers near 10.


I'm perplexed unless the suction lines, 2008 4 wire are leaking in a way that they're not leaking oil but letting air in. I'm going to try blocking off parts of the system to see if I can narrow it down some.

 

[willie59]

The return line, how does it enter the tank, does it drop oil in from the top or does it have an internal pipe that sends the oil back into the tank below the oil level line?

 

[fast_st]

Heya, the return line enters about centerline on the tank, 8 inches below the oil level, I built a box around the return line its maybe 5x5 square and 8 inches tall, the top has a 2x5 opening and the bottom is wide open, It does a pretty good job of slowing down the return flow and coaxing the air upwards, the bottom is a few inches from the bottom of the tank.

 

[old-iron-habit]

I'm wondering if you could be picking up air in the oil tank going to the pump. 25 gallon tank with a 28 GPM pump seem minimal to me. That oil is moving quite fast in your tank and may not be getting all the air out before being picked up again. Is your tank full?

 

[fast_st]

I'm wondering if you could be picking up air in the oil tank going to the pump. 25 gallon tank with a 28 GPM pump seem minimal to me. That oil is moving quite fast in your tank and may not be getting all the air out before being picked up again. Is your tank full?

Indeed, its a little on the small side by all the rules, but you'd have to shop hard to find a log splitter with a tank of 1:1 ratio between pump output and tank size, normally they're 2:1 with tank sizes from 4-9 gallons. With the footprint I have, its the biggest tank I could squeeze in with leaving a little air gap between the main beam and the tire. But there are a couple baffles and a diverter in the tank to slow the fluid flow down, coaxing the air up to the top

 

[mikebramel]

The suction line is way too small. You can help it by pressurizing the tank. Make sure your return drop is dropping close to the bottom of the oil.

 

[fast_st]

The suction line is way too small. You can help it by pressurizing the tank. Make sure your return drop is dropping close to the bottom of the oil.

I could not agree more, a 1 inch intake is way too small, my suction line is actually 2 inch, 4 wire low pressure suction line, it changes to 1 inch right near the pump.

 

[fast_st]

The return line, how does it enter the tank, does it drop oil in from the top or does it have an internal pipe that sends the oil back into the tank below the oil level line?

Atco, I do have a question regarding this problem. So I checked in at my local NAPA to ask about a replacement hydraulic suction filter and they mentioned the book doesn't list suction or return filters, just hydraulic filters. Now there is a bypass on this filter, a litttle piston and a spring, and its supposed to be a 30gpm suction filter. While its not leaking air, it might be restricting? It has 1.25 pipe fittings and the filter element is about six inches across and eight inches high and has no part numbers on it. I went shopping at Graingers and a few other outlets and I can't find anything even close to 30gpm in a spin on format. Best I can find is 5-6 gpm for suction line service. I'm wondering if the parts counter guy handed me the wrong thing? The company makes tank trucks and the like so they had all my weld on aluminum tank fittings and such. But a 30gpm return filter should have someplace near 2 inch fittings

 

[willie59]

Whoa, I didn't catch all this on the first read (admittedly I was likely under the influence of barley soda when I first read this thread). You have a 28 gpm pump and have fitted a bypass type hydraulic filter in the suction line. I can't say that this is the cause of your problem, but it's not a good idea. In theory, the suction side of a pump would be the ideal place to install a filter, low pressure, low velocity of oil, seems like the perfect place, but the drawbacks far outweigh the benefits, namely cavitation. Whenever you create a vacuum on a suction line you take the risk of cavitation of the oil which creates small gas bubbles in the oil. When these bubbles are exposed to pressure they implode violently and make tiny explosions, imagine miniature dieseling. You're far better off filtering the oil on the return side going back to tank. After all, if you insure the oil going back into the tank is clean (filtered), then the oil going from the tank to the pump would be already cleaned by the return filter and you don't risk killing your pump and other components with suction line cavitation.

 

[fast_st]

Indeed, it was supposed to be a 35 gpm full flow suction filter, it does have a poppet valve but I'm not sure of the opening pressure. I'm starting to think that its actually a 35gpm return filter and possibly a 4 gpm suction rated filter. What I was looking for when I built it was more of a suction screen as I couldn't readily find one to fit in the tank. Wix does have some filter offerings it seems in the 60 micron range that flow 79gpm with a stainless mesh media but the size is a lot bigger than what I'm seeing. Its possible that this isn't needed, the system is squeaky clean and using a nice tank breather to keep any dirt/water out.

 

[old-iron-habit]

Installing a return filter in a suction line can cost a lot of money. Any sales rep that says they are the same is not educated in hydraulics.

 

[old-iron-habit]

Indeed, its a little on the small side by all the rules, but you'd have to shop hard to find a log splitter with a tank of 1:1 ratio between pump output and tank size, normally they're 2:1 with tank sizes from 4-9 gallons. With the footprint I have, its the biggest tank I could squeeze in with leaving a little air gap between the main beam and the tire. But there are a couple baffles and a diverter in the tank to slow the fluid flow down, coaxing the air up to the top

Most log splitters have a lot smaller pump than 25 gallons per minute. Yours must really fly. I agree that a lower return line with baffle between that and the pickup would help keep air from being introduced as much.

 

[fast_st]

Installing a return filter in a suction line can cost a lot of money. Any sales rep that says they are the same is not educated in hydraulics.

Well, it was what the counter jockey handed over, what I needed was just the equivalent of a screen in a can in case someone pours in a bucket of ball bearings instead of a bucket of oil. I think I'm safe not having any pump input protection. The hyd tank was spotless when I built it.

 

[fast_st]

Well it should really haul ass but its never met the numbers, I'm thinking this filter assembly might be part of my dissapointment.

 

[fast_st]

Well, so a close out and final report, the porting of the pump was a success, the cross section of the flow area ended up with a 3x improvement, just a defect in pump manufacturing. It turns out that the cavitation and all the headaches when things were cold were caused by the supplied suction filter being wrong, instead of a 30gpm suction screen its a 5gpm suction filter or 30gpm return filter, gah!! F'd by the parts counter jockey. I've bypassed the filter after not being able to find a solid suction leak, also resealed the pump and torqued everything down snug. No more bubbles and the hydraulics move fast hot or cold.

 

[Jonas302]

What size bore and length is your cylinder and whats your cycle time sounds like a quick splitter

 

[fast_st]

Thanks, its a 5 1/2 bore if I recall, total stroke is 4' so it'll happily split anything. If I remember its 12 tons on the first stage and 30 tons on the second stage. Travel speed of the ram is about 1/2 foot per second maybe a bit more but more often than not I'm running it at idle versus wfo, it's just dandy at idle on the big wisconsin.