Americans are usually arrogant enough to think that all labor saving devices are invented here. In forestry equipment this is hardly the case. Historically much logging equipment was designed and built locally because local needs to harvest timber vary a lot. It is no accident that the giant yarders needed for the enormous trees of the Pacific Coast were conceived and built in the Pacific Coast area. Indeed some of the giant machines were virtually one of a kind designs.
As we have moved to an ear where much of the wood produced is essentially the result of plantation management, then we find that the type of machinery needed for that type of operation is far more uniform around the world, as plantation trees tend to be of uniform size, and the methods of handling them are pretty standard. This has permitted the appearance of truly international designs of equipment. Machinery appearing in this country under the name of 'Bell' is of this origin. Bell has been aggressive in making small wood harvesting equipment. As we understand it, the company is based in South Africa which the engineering and design work is done. They in turn outsource the manufacturing elsewhere (apparently Bulgaria is a popular location), and the end result is a truly international product.
What is fascinating is to see a product that is truly innovative, and this delimbing device qualifies. Small trees often have a lot of fairly small limbs which are very tedious to remove by hand with a saw or axe. The limbs on Douglas fir are fairly brittle and will often break off just in handling the log. However, limbs associated with Western Red Cedar, and Western Hemlock never break off, and old tricks like dragging another log over the top of them, burning them around a burn tree, running over them with the log skidder etc., simply don't get the job done. Similarly, a lot of thought has gone into trying to invent a mechanical gate or stanchion through which the logs could be passed that would strip off the limbs. The basic conclusion is that in order to be successful in stripping species such as the Cedar or Hemlock, you must have some sort of a device that reaches all the way around the tree and strips all sides, as you simply cannot get enough limb breakage during handling to clean up even one side of a log. This implies some sort of a device with moving parts.
Several people have tried to build limb strippers which would close mechanically in response to a log but no one has gotten the job done. Hydraulic closers work all right, but how do you control them and what do you use for a source of hydraulic pressure, remembering that these things are only used intermittently.
A Canadian group has for some years been marketing a machine functionally similar to the Bell shown here which actually has a small Diesel engine in it which runs a pump, but the unique feature of the machine you see here is that it is totally self powered. As you might guess, the arms to the back of the photo, have knives on them and once a tree is layed in the saddle, those arms fold down over the tree and as the tree is pulled through limbs are stripped cleanly all the way around it with the arms following the taper of the tree. The Arms are opened and closed hydraulically as well, but there is no engine in the basic design. Instead, your attention is directed to the 'spike wheel' in the foreground. It turns out that the 'spike wheel' is also the activator. As you bring the log forward and lay the butt in the saddle it presses down on the spike wheel. If the system is charged, the arms then close, and if it isn't charged, they will close shortly because as the log is pulled along with a grapple skidder (a swinging grapple works best) the spike wheel turns a hydraulic pump which charges an accumulator and / or closes the arms. Under optimum conditions, the accumulator will be charged while stripping one tree so it can promptly close the arms when activated by the next tree. If the accumulator is not precharged, the spike wheel will pump enough oil to close the arms while the log is advancing just a few feet. As a consequence the machine works best in trees that don't have limbs for the first 8 feet or so. The entire stripping stanchion is on a pivot so if you don't quite pull the log straight with the delimber, it can align itself with your operation.
We put a bridle on the machine and grab it up with a grapple skidder and take it down the skidroad to a convenient place outside the perimeter of the landing. We move it between landings on a flatbed truck. It is heavy enough that it will generally stay positioned while in use, and can easily be relocated with the swing boom grapple skidder as necessary when roads change or the pile of limbs gets too high.
As satisfied as we are with its performance, the design simply did not work for the fellow from whom we bought it. He first saw the machine when he was on tour in New Zealand and thought it was the best thing since sliced bread so he bought one. His problem was that he wanted to feed it with a log loader. This didn't work right because the log loader couldn't reach far enough to strip the whole tree in one motion, and when you stopped, the arms opened, and you lost your charge etc. He actually modified the machine to add an engine with a hydraulic pump so he didn't have to use the spike wheel, but when we got the machine we converted it back and use it as designed.
The message here is that this type of spike wheel activated delimber appears to work with a swing grapple skidder, but is not very satisfactory with a log loader.
I've talked about an 'accumulator', but unless you know something about hydraulics the significance of this device may pass you by. In its simplest form, an accumulator is a spring loaded piston in a cylinder. As oil is pumped, it pushes the piston back and compresses the spring. The spring will then keep the hydraulic circuit pressurized when the pump is not pumping (until the oil in the accumulator is all expelled).