Open-center axial piston pump adjustment

[WesRo]

Hi, newbie, but looking for a little expert advice by someone that knows more about this then me.

I have a 3.5 ton mini (jd 35g), I believe the pump is a open-center "constant horsepower" type, as there are only output lines and no feedback input.

Presumably this is the diagram for my pump https://www.miniexcavator-hydraulic-pumps.com/pdf/13-NACHI-PVD-1B-32P-11G5-wb.pdf (also see screenshot of pump diagram)

I feel like the pump runs hotter then it should, especially when I have the AC on (because the ac condenser is in front of the hydraulic oil cooler). I'm trying to find a smaller fan pulley or more aggressive fan, but I'm unable to find one, and now I'm thinking I should try to lower the pumps performance to see if that reduces the temperature.

Temp on the pump gets almost 80C on a hot day. I know some of you might say thats fine, but the oil is vg46 and gets a little too thin at that temperature. Ideally, I want this to run cooler.

The hex screw with the lock nut (see attached image) presumably controls the pressure on the bias spring, so I'm thinking the less pressure on that spring, the less flow the pump will make at higher pressure. Ideally I think the pump should make very little flow at the relief pressure.

So would it be safe to try adjusting the screw out (1/2 turn at a time) a few turns to see if that helps reduce the heat generating? I'm really not sure what other options they are...

TLDR: My pump runs too hot, is it safe to adjust the bias spring screw out so theres presumably less flow at higher pressure? Is there another way I can reduce the hydraulic temperature?

 

[Kjell]

No problem to adjust the torque screw, done it several times but i dont belive it will lower hydraulic temperature much. I owned a Hitachi zx33-5 for 8 years and used VG 32 oil without problem up to 25C.

With A/C on there is a magnetvalve providing pilot pressure to the pump regulation piston to lower the pump torque to prevent overloading of the engine. This make the machine slower and some operators dont like it and disconnect this funktion. I would start with this and also check the pressure of relief and shock valves. I guess you have cleaned the oilcooler.

 

[max s]

How many hours ?

 

[WesRo]

Hi @Kjell, you are exactly right on the solenoid valve providing pilot pressure to the back of the pump to lower the pump hp/torque when the AC is on. Mine is functional, I have verified this.

I have failed to mention that my mini is brand new, with less then 70 hours on it.

Also ambient temperature here is from 35C to 40C in summer. I'v herd hydraulic oil should be 38C above ambient, which would match up with the numbers I measured, but only when the AC is off. If the AC is on, it just gets way to hot.

 

[max s]

Assuming everything is working as it should considering it's brand new and depending on your location I would consider switching to VG68 hydraulic oil

 

[Welder Dave]

You don't want to do something that will void the warranty or potentially damage the machine. Thicker oil may help. The dealer may be the best place to talk to. You can't be the only one working in hotter temps. Maybe an aux. cooler could be installed?? I'd find it annoying if the hyd's. didn't respond as quickly as I wanted them to.

 

[WesRo]

I talked to my dealer before, and they basically said "its fine, it will alert you if it gets too hot". I asked if I should switch to vg68 and they suggested I dont, as vg46 is a good all rounder.

All my other equipment work just fine and dont get too hot or overheat, even my skid steer (which is 3x the hp of my mini x) does not ever heat at all.

I have found someone else saying they excavator hydraulics runs hot, and its using the same hitachi EX 46HN oil: https://www.heavyequipmentforums.co...perating-temperature-for-hydraulic-oil.30896/

He states it will go up to 78C (not sure if thats the tank, pump or cylinders), which for vg46 oil, thats about 10-11 cSt, which is a little too low for most pumps.

I think really the biggest issue on my machine is that the AC condenser is right in front of the oil cooler, and since the condenser is like 55-70C, the air coming to the oil cooler is already really hot, and then does not really do anything. Maybe the solution is just more air flow? I'v been trying to find a smaller fan pulley or a better cooling fan, if anyone has more info please let me know.

Also, I have noticed that the fan blade geometry is really odd, like the first part curves into the suction, I can post a pic, but that might be getting off topic.

 

[Kjell]

VG 68 oil is a good idea when its hot in the summer, but it will be impossible to start the machine when its cold in the winter because the pump is always in Qmax position at low pressure. My machine was delivered with VG46 oil and was impossible to start below -15C without a heavy booster and when it started there were leaks in the return hoses because of high backpressure at the returnfilter. This is the reason why i used VG32 oil. If the oil is to thin your first problem will probably be the high speed tracking stops working if your machine is equipped with Nachi travel gears like mine.

 

[Welder Dave]

If the machine alerts you when the hyd. oil is too hot I'm not sure how big of a problem you have. The dealer may have suggested the 46 oil as an all weather oil. It shouldn't hurt to run the 68 when working in hot temps. You would probably need to go to a thinner oil if you wanted to work in cold temps. It seems like trying the 68 oil wouldn't be an overly expensive way to see if it runs cooler. Another option is maybe you can add an additional electric fan to help cool the hyd's.