So I'm messing with another old machine and again looking into a possible hydraulic issue. At idle and low speed there is a thumping noise that you can hear/feel. I traced it back to one of the pressure lines coming off of the tandem pump (similar set up to the pump i posted pics of a few weeks back.) I was told this pump was fairly new.. could this thumping be air thats being compressed in the pump? The pump is a tandem and the thump can only be felt on one outlet, if the pump was drawing air i would think you'd feel it on both..? What else could this be? it goes away once you throttle up.. I think the pump is a vickers again.. any thoughts?
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Crane is thumping, air in hydraulics??
- Thread starter mrusso94
- Start date
Lashlander
Senior Member
It sounds like you have an accumulator that has lost its Nitrogen charge. Without the Nitrogen pressure to cushion the oil the pump bypass valve will surge in and out. Does it have a pressure gauge? You should see the pressure surge. Seems funny it goes away though when you throttle up.
No pressure gauge.. I would think I would feel it in the hydraulics if the bypass was surging in and out, all operations are as smooth as ever.. and this only occurs at low RPM.. also, its only off of one side of the tandem pump.. I'm wondering if its something in that end of the pump, maybe a vane hanging up in the rotary group that comes out at higher rpm?? sounds crazy I know, just seeing if anyone has any ideas before I go tearing into this thing. And for what its worth, its very inconsistent, it does it one minute, then the next its fine... sometimes its very faint, sometimes very intense.
maytag
Well-Known Member
- Joined
- Mar 18, 2010
- Messages
- 124
- Location
- saraland al
- Occupation
- Hydraulic technician in a steel mill
You didn't mention your engine rpm other than idle/low-older vickers pumps required 600 rpm for minimum speed.
Tom
Tom
No tach on this machine, though i'm certain its above 600. Also, it idles the same speed it always has, idle rpm hasn't changed.. In addition, there's two pumps on this machine and only one seems to have an issue..
sea_goin_dude
Member
maybe a vane hanging up in the rotary group that comes out at higher rpm??
I must ask did this problem just start or maybe just bought it used. and the problem was there from the start.
I dont think a vane would hang up but I have seen a vane in a pump or hyd motor break and lock up the pump/motor, the broken vane will lock up the device but you can take one vane out and run until you get another one but it will definitely jump/chatter. I would check and make sure all the vanes are there. I had to remove a vane (broken) on a hydraulic motor years ago and it ran until I could get another cartrige but it did jerk/chatter at slow speeds. Just an idea but I would check. Pump vanes are held OUT by centrifugal force from the motor but hyd motor vanes have springs to hold them out as there is no cent. force at start to get/hold them out.
I must ask did this problem just start or maybe just bought it used. and the problem was there from the start.
I dont think a vane would hang up but I have seen a vane in a pump or hyd motor break and lock up the pump/motor, the broken vane will lock up the device but you can take one vane out and run until you get another one but it will definitely jump/chatter. I would check and make sure all the vanes are there. I had to remove a vane (broken) on a hydraulic motor years ago and it ran until I could get another cartrige but it did jerk/chatter at slow speeds. Just an idea but I would check. Pump vanes are held OUT by centrifugal force from the motor but hyd motor vanes have springs to hold them out as there is no cent. force at start to get/hold them out.