The convenience of being able to alter tyre pressures while on the go, to ensure the correct operating pressures for field or road work, is now a reality with a retro-fit central tyre inflation system.
Jane Carley finds out what is involved.
Maintaining correct tyre pressures for field and road work is an ongoing challenge for many farmers and contractors, especially as machinery is expected to perform efficiently in-field and then travel at higher speeds on the road.
Correct operating pressures minimise the tyre’s impact on soil and save fuel in the field by reducing wheelslip, also prolonging the tyre’s life. As tyres get increasingly technical and more expensive, the latter is even more of a priority.
In an ideal world, low pressures are used in-field to spread load and increase traction, while high pressures are used on roads for increased stability and greater fuel efficiency. Unfortunately, manually altering tyre pressures is a long and tedious process.
However, several manufacturers, including Fendt, Claas and Mercedes, have created machines with central tyre inflation systems (CTIS).
But while this is great for altering tyre pressures on the go, it is not a widely available technology and is an expensive option.
Thankfully, there are various retro-fit kits which will allow you to do this, and one such supplier and fitter is UK firm TractAir.
It is a major supplier of air braking systems to tractor OEMs as well as offering retrofit kits, and last year it started marketing a CTIS based on the compressor equipment used for air braking.
Director Nick Constantine says: “It is a natural progression, but we need to be able to take air out of tyres as well as put it in, so a greater degree of control is needed than simply pumping tyres up using the compressor.
“There were a number of systems in existence to maintain pressure designed for commercial vehicles or for military applications, but they were not ideal for the demanding, often dirty agricultural environment.”
Working with German specialist PTG, TractAir is offering a system for tractors featuring an electronic control unit which can be used in-cab, allowing the operator to alter tyre pressures when moving from road to field, for example.
The firm can fit the systems at its headquarters at Brough, East Yorkshire, or can supply full kits and instructions for fitment by a dealer or farm workshop.
The kit includes bespoke brackets for fitting outboard systems to the wheel hub, plus common valves, pipework and rotary unions.
Control is via a portable dedicated box or can be integrated into the tractor’s IsoBus terminal.
To eliminate external air lines, tractors with bar axles can be fitted with internal rotary unions, keeping all pipework hidden inside the wheels.
This is also possible with trailers, and BPW and ADR have axle designs specially drilled to take air through the centre of the axle.
In addition to tractors, TractAir can supply systems for trailers, sprayers and forage harvesters.
The manufacturer’s systems can also be swapped between tractors, allowing the CTIS to be removed from a tractor being sold out of the fleet and switched to a new model.
To see how it is done, we joined the company as it fitted a CTIS to a 2014-plate Fendt Vario 724 and 20-tonne Fliegl push-off trailer, which has sliding axle weight transfer and will also be used with a muck spreader attachment.
The customer, a Lincolnshire farming enterprise, plans to use the trailer and spreader for contract work as well as on its own land, requiring frequent roadwork and regular variations in tyre pressure.
Alan Wattam, TractAir’s senior design engineer, says: “It is quite an ambitious project but there is no reason why a business cannot build it up over a couple years, starting with the tractor and adding the compressor and trailer once the benefits have been evaluated.
“CTIS usually takes about a week to install, but once we have designed the brackets we can supply the system as a retrofit kit which can be installed by a local dealer or a competent farm mechanic.”
Prices are from £4,335 for a tractor system with front and rear external fittings, where required compressor prices depend on specification.
TractAir also offers simpler, workshop-based inflation and fast fill kits which help demonstrate the benefits but do not offer on the move changes.
Rotary unions to connect the air delivery pipework to the valve are fitted to the wheel using bespoke brackets for each tractor brand or wheel type.
Air is delivered via a dual line system; the small bore control line opens the pneumatically controlled check valve, while the high flow line puts air in to the tyre or takes it out.
A single line could lead to a loss of pressure overnight via small leaks in the system.
Seals and air lines are only pressurised when altering the tyre pressure, minimising their duty cycle and extending service life.
A priority valve ensures that the maximum pressure delivered to the inflation system is 6.5 bar, so there is always sufficient pressure to activate the air brakes.
Air storage tanks are pressurised up to 8.5 bar, so the valve prevents air going to the CTIS until the pressure comes back up.
Using the tractor’s compressor is sufficient to inflate the tractor tyres, but a separate compressor has been supplied for this tractor for use in transport operations with a CTIS equipped trailer.
This hydraulically driven compressor delivers air at 4,000 litres/min, and is mounted on the front linkage, where it can be fitted with wafer weights to also add ballast.
The valve box can be mounted in a number of locations and provides the electronic to pneumatic control, taking air from the air brake line as required, and as dictated by the priority valve.
Pipework can be protected in hazardous areas such as alongside hedges by disconnecting from the rotary union and valve and slotting into storage sockets on the fenders.
The control box allows the operator to select the axle and switch from road to field pressure settings or vice versa.
Deflation for 710/70 R42 tyres from 20psi to 12psi is 90 seconds; inflation from 12psi to 20psi using the standard air brake compressor is six minutes.