By Bill Adams
Twisted Vanes
The other day, I read an advertisement that mentioned a “twisted vane vacuum cast impeller” on a centrifugal pump. It mentioned the twisted vane, but it didn’t describe it. Perhaps I’ve been out of the fire service too long, but I don’t know what the hell a twisted vane is and why it is better than an untwisted vane. So, I challenged Jason Darley—my go-to person for fire pumps—by saying it’s your ad about your pump, but it doesn’t say what is so special about twisting your vanes. I added, “Just give me the facts; keep it simple; no Safespeak, and don’t knock the competition. What is the difference between twisted and untwisted vanes and are all impellers vacuum cast?”
Jason responded: “Bill, we put a lot of love into our impellers at Darley. Overall, the twisted vane is a more efficient design than a straight vane. This has been a Darley design principle dating back to the early 1930s, when we had an engineer by the name of Pete Yates who was a mastermind impeller designer. The pitch and shape of the twisted vane is similar to what one would see all summer while driving along the highways of Wisconsin—the propellers on a boat motor. I know you former New Englanders have a similar boating season so I’m going to challenge you to send me a picture of a straight prop blade. In both cases, the pitch and the curved shape in the leading edge of the vane is more efficient as it propels the water keeping the energy focused on the intent. The ultimate outcome for the firefighter is a smoother, more compact, and more efficient product.” He got me on that one. But he could have just said it moves the water better like a boat’s propeller.
He kept on, “In the case of vacuum casting, simply, we take the air out of the equation. We use an aluminized bronze, which is an extremely hard variation of brass. Keeping the air out of the equation eliminates “porosity,” which is air bubbles in the finished product. Porosity can lead to a number of challenges and failures in something spinning at thousands of revolutions per second that can be exposed to all sorts of foreign materials beyond the water the product is intended to move. The hard bronze eliminates the need for us to use a third process of heat treating and ensures the entirety of the impeller is extremely hard. We also broach our impellers, which allows them to slide on to a splined stainless-steel shaft, with no moving parts (like a single key) holding the two critical components together. With up to 11 splines, the Darley impellers stay exactly where we and our customers prefer: fighting fire. As you know, I could go on all day, but I’ll kick it back to you if there are any questions I can answer.” Jason will keep answering a question until he’s sure you understand it.
SafeSpeak
Now, I’m not talking about Darley here because he usually nails a question when you ask it. Did you ever ask a fire truck vendor a simple question and get a verbal runaround? I asked one a question the other day that could have been answered with a simple YES or NO. Instead, the vendor babbled like a brook for 10 minutes…and never answered the question! It happens quite often when a person is asked a question he does not want to or can’t answer. Sales and marketing people excel at it.
Whenever I think I’m going to get a verbal “sleight of hand,” I always ask the question in writing, hoping the person’s fingers will tire typing while evading answering. Later, I’ll expound on the dangers of using SafeSpeak and TechnoSpeak in the fire apparatus purchasing arena.
See Ya Later, Chris!
After a 10-year run with the Fire Apparatus & Emergency Equipment magazine, Senior Editor Chris Mc Loone has pulled the plug, and not the hydrant