Monday, April 28, 2008

Zen and the Art of Icemaking - Part 3

My Zamboni driving experience has been primarily with two models - both very old and very new. I learned on a 1969 model HD-B Zamboni. This model is very recognizable to most people as the classic Zamboni look and was widely produced. Later, the 500-series models came along. There have been several variations but the basic look and shape is the same.

Here is a classic white-over-blue HDB:


Compared to driving a 500-series Zamboni, the HDB is more like driving a standard shift car versus driving a car with an automatic transmission. It's different as to what is going on, but a similar comparison of actions.

For controls, the HDB has a steering wheel (of course) and a brake pedal (they never work), a gas pedal, and a transmission lever. The hydrostatic (hydraulic) transmission is like that of a military tank, the further you push the lever, the faster it goes. The lever has a neutral position; you pull it sideways left and push forward for forward speed. For reverse, you push it sideways right and pull back.

The gas pedal makes a difference on speed as well; more gas = more speed. So, the top speed of the Zamboni of 9 MPH is achieved with the lever fully forward and with maximum gas pedal (without blowing up the engine).

It gets tricky while resurfacing, with all the hydraulic conveyors working to move snow up into the dump tank. During resurfacing operations, it is critical to keep the engine RPM's at about 2700 RPM. This ensures that all the snow keeps moving nicely and the engine has power to drive the machine while moving the snow. If you go too high on RPM's, you risk damaging - even blowing up - the engine. Bad news, for sure.

But if you let the RPM's drop, the snow doesn't move through the conveyors and the whole thing gets bogged down. That is ugly is well.

The solution is that the operator constantly has his right hand on the transmission lever. When he or she needs to slow down, the lever is pulled back as the gas pedal is reduced, keeping the RPM's the same while slowing speed. The same when he needs to speed up - more lever and gas at the same time. It can get really tricky in the turns where, as previously mentioned, the operator is also raising the blade a little, backing off the water a little, trying to maintain the icemaking pattern, and not crashing into the boards or on-ice crew.

And then, as he wants to speed back up for the straightaway, he is lowering the blade, turning the water back on, while giving it more gas and transmission lever.

That's the comparison to the standard shift, clutch, gear, steering, watching the road, etc.

Believe it or not, I actually prefer the HDB, with all the complications. I guess it is because I learned on this model, it's what I'm familiar with and I prefer the sense of control over the machine.

But, for mass distribution, ease of training new operators, and in the face of competition from other manufacturers, Zamboni developed a much easier control system with the advent of the model 500 and future models.

Model 500 Series:


These models employ a throttle setting that holds the engine at the specified RPM so the operator does not have to. He only has to worry about speed control. Early models did not perform well and were finicky with speed changes. If you sped up or slowed down too suddenly, the throttle/governor control could not stay adjusted properly. Later models seem to have solved that.

The model 520 at USBA has a second lever by the transmission control lever. This is the throttle. The "gas" foot pedal is actually not a gas controller at all. It is really a clutch on the hydrostatic transmission. It works the opposite of a clutch on a car; he clutch is fully engaged when the foot is off the pedal, and disengages the clutch as the pedal is depressed, allowing the machine to go faster.

The transmission lever still can control top speed, but operators usually just push it all the way forward and control speed with the pedal. So when the operator comes out on the ice, he pushes the transmission lever fully forward, and then sets the throttle at about 2700 RPM.

Then he lowers the conditioner and proceeds with the icemaking process. He uses the foot pedal to control speed, even though it is a clutch and not a gas pedal. Even the newer designs do require the operator to change speeds gently, but it is not as bad as the earlier models. I'm sure even those models worked well when properly adjusted, but they seemed vulnerable after some use.

As I come off the ice at USBA, I turn off the conveyors right about when the front wheels start to go off the ice. Then I pull back on the throttle a little bit, to let the engine rest, but not too far because I want strong power to the hydraulics so I can lift the conditioner about the time when the back wheels get to the edge of the ice.

Then I pull off the ice and pull the throttle back to about 1500 RPM to drive back and dump the snow from the tank.

The 500-series machines' most distinctive change is to the snow tank. You can see it looks different, and it also has a larger snow capacity. This allows operators to shave off a little more and give better ice without as much fear of filling the snow tank before finishing.

Other incarnations of the 500-series have slightly different controls, but the concept is the same.

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