Setting suspension accumulator pressures for the perfect ride.

Colliedog

Member
Location
Dorset
*Whilst this post is based around the CNH Terraglide 1 system the principle is the same for all hydraulic suspensions and the discussion is open for various machines.*

I have heard from many people that the latest Terraglide on the newer 4B tractors works very well but I think its fair to say that the original setup never worked as well as we would have liked. I wrote a post on here last year on how to fit cab air suspension to New Holland tractors https://thefarmingforum.co.uk/index...sion-upgrade-for-new-holland-tractors.299452/ Since then I have been playing around getting my front suspension to work better on my T6.160.

I was fortunate enough to get my hands on a genuine New Holland dual accumulator upgrade kit. This made quite a difference but I have been told by several people that changing the pressures improves the ride. The problem has been what to change the pressures too?

I did quite a bit of research on various forums and the internet and it all got quite confusing as some say they found improvements with higher pressures and some believe lowering pressures makes the ride softer. As I didn't find the answers I was looking for I decided to search further afield and to the inventors of Hydro pneumatic suspension, Citroen. Citroen have been using this system since the 50's and allowing other manufactures such as Rolls Royce to use the technology before it found its way into the construction and agricultural fields. I went onto a Citroen car forum and found all the same arguments for whether to use higher or lower accumulator pressures that I was finding for tractor suspension. I then had a breakthrough by finding a very clever Citroën engineer from the Netherlands who made the whole tuning processes very clear. He said the best way to make the ride smoother is to change the valving. This is easily done on a Citroen as the valve is a simple disc type check valve at the base of the accumulator. Bigger orifice for a smooth ride, small orifice for a firmer sporty ride, but bigger accumulators at the correct pressure can also achieve a smoother ride. The valve chest on tractor front suspension is quite a complex and expensive item so I thought that was best left alone leaving the solution to increase the hydraulic damping volume in the system...

As the gas and oil pressure within a hydraulic accumulator will always be equal they work at their best efficiency when the chamber is 50% oil and 50% compressed gas which kind of makes sense. The tricky part is what pressure to pre-charge the accumulator in order to achieve this. There is quite a complex scientific equation to work this out but as we are using an inert gas (nitrogen) and we forget about thermal expansion we can simply say that the pressure of the gas doubles when the chamber size is halved. Or in simple terms the pre-charge pressure is half that of the oil pressure in the hydraulic system.

The next step was to find out what pressure was inside the hydraulic system of the front suspension at varying loads so a remote gauge was connected to the system.

IMG_2988.jpg IMG_2990.jpg

I measured the front axle weight on a weigh bridge and took systems pressures at varying loads to give a full spectrum of what the suspension had to cope with which are as follows.

No front loader drill on back - axle weight 830kgs - system pressure 23bar
No front loader nothing on back - axle weight 2780kgs - system pressure 60bar
Front loader fitted nothing on back - axle weight 3460kgs - system pressure 85bar
Front loader fitted with grab nothing on back - axle weight 4420kgs - system pressure 105bar
Two silage bales on loader nothing on back - axle weight 5250kgs - system pressure 145bar

As you can see it is a lot for one accumulator to cope with. This was the point where everything started to make sense. The dual accumulator kit had given an excellent ride when running with an implement on the back or driving around with the loader on the front and even better with a grab on the loader but if the loader came off the ride became harsher again. The two accumulators fitted to my tractor were pre-charged to 15 bar and 60 bar meaning the system had a lack of damping at 60bar hydraulic pressure. Suggesting a 30 bar accumulator would give a smooth ride for an empty tractor. As the tractor spends most of its life with the loader on I decided to keep the 60bar accumulator and add an additional 30 bar accumulator. This then in theory covers me for the very wide range of front axle loads my tractor experiences.

IMG_2995.jpg

There is now a total of 3 litres of accumulators damping the suspension which is almost too much as you can see the axle self levelling on loader work sometimes, but the ride is now incredible. You can see the axle moving absorbing the bumps no matter what weight is fitted to the front of the tractor. Even hitting plough furrows with 20psi in the front tyres you cant feel anything until the rear axle passes over it. The damping control from the Terraglide valve block is very good at controlling bounce on the road and the extra capacity from the accumulators provides very smooth stable control for road work .

I hope this Knowledge I have gained will help others set their tractors up to ride as well as mine. I know there are a few of us already playing around with accumulator pressures and I feel I have started a post where lots of useful information can be shared here. So on that note can I suggest we keep this post for useful questions and answers on the subject rather than individuals opinions on various types of tractor suspension. There are lots of reasons why manufactures don't do this to start with including cost, reliability, servicing, safety etc, etc. not to mention everything engineering can be improved!
 
A very interesting read, thank you for sharing.
So the higher the pressure the better damping at higher weights
The Lower the pressure better when lighter?

I'll read it again... to make sure
Thank you
 
That’s correct. So if the pressure in the ram was 40 bar the system would ride best with an accumulator preset at 20 bar.
Ahh great So basically take average of your pressure at its working state/range then try to halve the pressure bar roughly to obtain a accumulator pressure
Obviously the wider working range the more accumulator you'll need to even it out I'd guess?
 

del_boy

Member
Location
Herefordshire
Ahh great So basically take average of your pressure at its working state/range then try to halve the pressure bar roughly to obtain a accumulator pressure
Obviously the wider working range the more accumulator you'll need to even it out I'd guess?
Ive messed around with these nh accumulators a fair bit on 3 tractors over the last 2 years, different pressures and even put bigger accumulators on but the best ride i think is the one i put 2 accumulators on set at different pressures.
I did think about adding 2 extra small ones on the ends of the pipes where they come off the ram but was only an idea.
You done well to get 3 tucked away inside the back wheel, theres not alot of room.
Have you fitted your upgraded air cab shocks on this tractor?
 

Colliedog

Member
Location
Dorset
Ahh great So basically take average of your pressure at its working state/range then try to halve the pressure bar roughly to obtain a accumulator pressure
Obviously the wider working range the more accumulator you'll need to even it out I'd guess?
It’s just the static pressure in the system when it’s not moving. Working fluctuations are absorbed by the accumulator. The problem on a tractor is the varying weight loads, if we never put any weight on a tractor the science would be a lot more simple.
 

Colliedog

Member
Location
Dorset
Ive messed around with these nh accumulators a fair bit on 3 tractors over the last 2 years, different pressures and even put bigger accumulators on but the best ride i think is the one i put 2 accumulators on set at different pressures.
I did think about adding 2 extra small ones on the ends of the pipes where they come off the ram but was only an idea.
You done well to get 3 tucked away inside the back wheel, theres not alot of room.
Have you fitted your upgraded air cab shocks on this tractor?
You can’t put accumulators next to the ram as that is the wrong side of the damping restrictor valve which acts as the shock absorber. If you did the result would be like a car with the shock absorbers removed ‘very bouncy!’ Also putting one on the other side of the cylinder would be a waste of time on Terraglide 1 as there is neutral pressure that side of the cylinder. Terraglide 2 as fitted to the tier 4b tractors has an accumulator fitted to both sides of the ram but in order to get this to function the lower side of the cylinder is pressurised to 55 bar then both accumulators are pre charged to 30bar with a larger 2lt accumulator on the top side.
I know you have one tractor with a 2ltr accumulator on it. Do you know what pressure is in it as I recon if we could find your front axle weight we could find a pressure to make that work really well.
yes it is the tractor on air cab suspension. Have you fitted yours yet?
 

Phil P

Member
Arable Farmer
Location
North West
On the later Deere front suspension (30 series onwards) they use a system where pressure can be hydraulically increased to both sides of the rams. This keeps the neutral position but increases the pressure in the accumulators and stiffening the ride. The larger models (8 series) have automatic dampening and lockout valves which work in conjunction with the brakes and hitch to stop the front diving or lifting. It’s a very clever but complicated system.
 

cosmagedon

Member
Location
North Wales
Another good mod you've done [emoji106][emoji106]

I still haven't fine tuned my accumulators, I've been meaning to see what hydraulic pressure I've got on the front but it's something else I just haven't got around to, I think the fittings I need are still in my eBay basket!
 

Colliedog

Member
Location
Dorset
On the later Deere front suspension (30 series onwards) they use a system where pressure can be hydraulically increased to both sides of the rams. This keeps the neutral position but increases the pressure in the accumulators and stiffening the ride. The larger models (8 series) have automatic dampening and lockout valves which work in conjunction with the brakes and hitch to stop the front diving or lifting. It’s a very clever but complicated system.
That’s really interesting. Obviously all systems increase the pressure as weight is added and the system self levels, but If the system uses an adjustable pressure valve to always maintain a high pressure in the cylinder and accumulator you could use one accumulator to do the job of the three that I’ve used on mine. I’m just wondering if that’s how the later new Holland systems work. It’s quite hard to work out from a workshop manual!
I think a lot of the current tractors use various inputs to electronically control the suspension. There will be some clever people who will able to upload improved logarithms via a laptop but this is way beyond me! There are still lots of older type passive systems about that can be improved just by changing a pre charge pressure.
 

Colliedog

Member
Location
Dorset
Another good mod you've done [emoji106][emoji106]

I still haven't fine tuned my accumulators, I've been meaning to see what hydraulic pressure I've got on the front but it's something else I just haven't got around to, I think the fittings I need are still in my eBay basket!
The chart I have posted covers the suspension as fitted to Tm’s, T6000’s T6’s, swb T7’s and the Case equivalents. So if you know the front axle weight you can use the chart to work out the optimal accumulator pressure. I can’t help but think that simply pumping to standard accumulator up to around 30bar would make a big improvement to theses models but this would make the suspension very hard if you were carrying an implement on the linkage. Maybe a twin accumulator set up of 15 bar and 30 something bar would be most people’s answer.
However I think you have a Lwb T7 though? I would also like to know the hydraulic pressure in there. We have got a couple that I don’t drive but I can’t see any where easy to tee the gauge into.
 

ColinV6

Member
I bought a 600kg weight block which I plan to use all the time. It’s made the ride noticeably better. Not perfect as such, but a huge improvement on before.
 

Flat 10

Member
Location
Fen Edge
I bought a 600kg weight block which I plan to use all the time. It’s made the ride noticeably better. Not perfect as such, but a huge improvement on before.
An accumulator in the FL suspension can be good. Poor mans front suspension. Not sure how it would interact with tractors own suspension as only used them on standard axle tractors.
 

ColinV6

Member
Does the suspension self level, out of interest, as the tractor seems to sit better. More nose in the air. With the block on the front?
 

Colliedog

Member
Location
Dorset
Crazy how it looks like you alone have spent more hours improving the comfort of New Hollands than New Holland themselves.
Manufacturers spend years developing these systems. I will find a photo out later to show you how long ago it was developed before going into production you will see it wasn’t even New Holland that developed it. My tractor is now 4 years old and was one of the last to be fitted with terraglide 1. The new systems are much better and continuing to be improved. The new T8 coming out this year uses a semi active skyhook front axle that sends signals to a processor that controls 4 semi active accumulators on the cab which absorb the bumps and keep the cab from pitching and rolling. It will be a while before it comes down to the smaller tractors but it sounds very promising!
 
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Colliedog

Member
Location
Dorset
I bought a 600kg weight block which I plan to use all the time. It’s made the ride noticeably better. Not perfect as such, but a huge improvement on before.
Your just the sort of person this post is here to help!
You don’t need to carry a weight to get it to work. If you or someone with a Swb T7 can get a front axle weight of ‘the tractor only’ no weights or trailers or implements we can work out pressure to make the suspension work better
 

Update on the Sustainable Farming Incentive pilot

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Update on the Sustainable Farming Incentive pilot

Written by Lisa Applin

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In July, we opened the applications window for farmers to join our Sustainable Farming Incentive pilot.

The Sustainable Farming Incentive is 1 of the 3 new environmental land management schemes. It sits alongside the future Local Nature Recovery and Landscape Recovery schemes.

Through the Sustainable Farming Incentive, farmers will be paid for environmentally sustainable actions – ones that are simple to do and do not require previous agri-environment scheme experience.

We are piloting the scheme to...
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