Big Blue Cast Iron or Stainless Steel? Lots of holes, or a few large holes? Does anyone think older wash arms did a better job, or are today's wash arms desgined for the low water use a better deal?

Also what was the rationale behind those cast iron wash arms? Cast iron will eventually rust, not the sort of thing I'd want spraying around my dishes.

L.

The cast iron Big Blue arm was "epoxy" coated and should not rust under normal conditions.The 4-way stainless steel HydroSweep really was more powerful.Any old spray arm system beats todays tinkling waterhose systems in power.Modern machines compensate with obnoxiously long wash cycles and better filtering systems.

Cast iron will rust - the wash arm in my KD2P rusts a little inside - but unlike steel, cast iron rusts in particles not flakes. So the rust particles are easily flushed away in the pre-purge. After that, the water is very clear. And iron rust particles are basically of very low toxicity. Not to be taken in mass quantities, but a trace amount is probably healthy.

One possible advantage of the heavy cast iron wash arm is that it uses a simple bronze bearing with no need for anything to keep it from floating off the bearing - the weight of the arm keeps it on the spout. It does pack quite a wallop though.

Kitchen Aids they had to put large heavy metal door locks in the doors. As the power of the cast iron spray arm is so great at 50 gallons/minute that not only is the grime blasted from the plates but the plates themselves are SCREAMING to get out of the dishwasher! So they have to be bolted inside the machine so that they don't escape.
My arm is 40+ years old and I don't see any rust. Cast Iron rusts to the surface and that acts like a barrier to further rusting.

The Hobart cast iron wash arm was the wash arm used in commercial machines. They did not fail. The larger bronze bearing held much better in cast iron than the smaller one holds in the Bakelite. The wash arms at the top of the tank in the commercial machines had a hole in the hub for the bolt and nut assembly that held them in place. The cast iron also developed a film of oxidation and minerals that protected the cast iron from further oxidation where it was not coated. The 4 Way Hydrosweep which debuted in the 15 series has a much smaller and different style bearing and support system. The Bakelite hub wears as this bearing fails and usually the wash arm support and the wash arm have to be replaced. When the bearing wears, it not only allows water to spray out under the hub, but the wobbling arm destroys the support. If people put dishes with enough food soil in the dishwasher, don't over use detergent and don't have their water heater set to 160F, the wash arm and support can last for decades. The test to see if the wash arm needs replacing is to give it a flip of the hand while it is dry and watch how it spins. If it spins smoothly and freely and coasts to a stop, it is fine. If it makes noise and shudders instead of spinning, it needs servicing. Finally, the taller tub of the 15 series mandated a shorter motor & pump. The 14 series had to pump with greater force to make the larger sprays forceful enough to wash well and it used more water to keep the sump full enough to supply that powerful pump that was moving a lot of water. If you remember the first GE wash arm machines had a wash arm with the raised bumps surrounding the slits in the wash arm similar to the Hobart design. They were absolutely miserable at washing because they did not have a filter like the KitchenAids and their cheaper motor ran at half the speed of the Hobart motor and powered a much less efficient pump. The 15 had less space under the tank and made up for the design by having the pump force water through smaller holes to give more power. Hobart did give the smaller holes a design tweak in that each hole is surrounded by a slight dimple that forces the column of water to fan out into a wider pattern than the hole from which it emerges

As to performance, the 4 Way Hydrosweep was needed to wash in the larger tank. The finer holes allow water to be directed in precise patterns. The Big Blue Hobart Wash Arm produced "6 Moving Walls of Water" which were very effective in the smaller tanks up to the 15 series, although the water distribution did not give the more surgical precision of the Hydrosweep. The fan spray had advantages. For instance, I would place the wire rack from my Farberware Open Hearth Broiler on the center row of loops in the lower rack of the 14 and prevent it from tipping by putting the body of the broiler over it. In a normal wash cycle with the two detergent washes and three rinses, the 14 with the fan-shaped spray pattern cleaned the rack uniformly while the 18, with the rack in the same position in the lower rack and the more precisely directed spray pattern left some small places that needed further cleaning. Perhaps if I were to bother to rest it over saucers to hold it a bit higher, the water pattern would even out to be more like the fan spray of the 14. I use one of the Jenn-Air ceramic fake briquette plates under the heating element of the Farber to give a small amount of smoke flavor to the generally very lean foods cook on it and that washes well in both machines, just standing in the rack, but angled to that the soiled side faces down, the reverse of the way plates would face in the rack.

I think the early machines tended more to clean with water pressure, heat and detergents whereas modern machines clean with warm water and detergents.
When you use modern detergents in the KAs from the mid-60's, they run rings around the newer machines - same or better cleaning results in less than 1/4 the time.
But those high pressure jets probably were the reason for the cast iron design. I think the pre-Whirlpool KAs were designed by engineers who only cared about function and used whatever material achieved their purpose best.
I notice that my Miele's, which use stainless steel arms, usually start to show bearing wear after only 15 years or so.

Here on Cape Cod there are still alot of UM-4s(1950s-early 1960s) still up and running. The seasonal restaurants say if they bought one 30 years ago they only have actually 15 years of use. I mention the UM-4 as it uses the cast iron (Hobart used to call it NiResist) washarm. The machines are so quiet all you here is the rhythem of the RPMs of the wash arm spraying the water. The WM-1(Mid 60's) has the 4 way HydroSweep and is more styled after the later KitchenAid machines with the push down handle and Stainless Wash Chamber.
The UM had a much smaller wash chamber and gravity drain as the WM was a KitchenAid sized chamber and a pump drain. Both machines clean extremly well. UM is a 3 1/2 min cycle and the WM is a 4 min cycle. I'd love to get my hands on either a top loading portable or front loading portable with a cast iron arm.

Here is a classic UM4 dishwasher on EBAY.. Would take some TLC to make it look really nice, but it does have all the panels so it can even be a freestanding unit. In the right installation, you may not even have to worry about the gravity drain.