Straw Shredders, Bigger is Best

Teagle Machinery Ltd, based in Cornwall, has been supplying the agricultural market with a wide range of equipment for over 40 years. Now enjoying worldwide success, their “Tomahawk” trailed straw shredder feeders have found new markets in North America. Typically, the American agricultural market demands very large hydraulic flows, utilising larger tractors to work larger areas at greater speed. Even the crops being shredded for fodder are tougher! This ‘bigger’ demand also brought into focus the topical question of energy efficiency – wasted heat energy had to be reduced, not increased.

Bale shredder

This presented a problem for Teagle as the standard Tomahawk machine was designed for the European market and the Americans were anxious to take delivery without delay. Teagle approached Hydraulic Projects Ltd (Hy-Pro), their supplier of solenoid spool valves, with a request for the current valve to have the priority flow divider capability increased from 30 to 60 l/m, using existing electronic controls.

Barry Wynn, Hy-Pro’s Chief Designer (formerly Chief Designer to David Brown Engineering) instigated an immediate test program to validate the possibility of modifying the existing 30 l/m flow rating to 60 l/m. The first prototypes were despatched within 5 weeks to allow machines, modified to run at high speeds, to be field tested in the UK and the USA.

Hy-Pro engineers attended the field testing, data logging the performance of the hydraulic circuit. This was analysed and was used to design a new proportional flow dividing section using the existing solenoid coil and armature with a new proportional cartridge and manifold. The new valve achieved a 20% lower pressure drop P-T with a 30% lower pressure on the priority side, the orifice cartridge opening at under 12 bar instead of the previous 28 bar.

Solenoid valves

Hy-pro engineers also identified an unacceptable pressure drop through the existing pressurising cartridge used to power the pilot operated solenoid sections. Barry Wynn was now tasked to replace the existing 3 pressurising cartridges for flows of

1-15, 10- 45 and 30 – 60 l/m with a single cartridge to handle flows of 1-60 l/m.

The new cartridge design uses a reciprocating piston, proto type parts were manufactured and tested in house on flows up to 100 l/m. The new retrofitable cartridge resulted in reduced pressure losses from 71 to 42 bar and was much quieter in operation. As this development was running simultaneously with the new flow dividing section, both new designs were incorporated into production machines within 15 weeks after the initial inquiry.

Hy-Pro’s ability to rapidly develop bespoke valves means its customers can take full advantage of opportunities as they arise. In this case the new design, with much improved efficiency, allowed Teagle Machinery to expand into a new market in North America. Interestingly, the field testing of the new faster machine on UK farms highlighted the advantages of increased output from the Tomahawk, discovered in the USA, and has now been adopted on all EU machines.

For more information, please call:

Alan Wilson

Hydraulic Projects Ltd

Dawlish Business Park, Exeter Road, Dawlish,

Devon EX7 0NH

Tel. 01626 863634 Fax 01626 866283