QUESTION:
Does it make any sense to put stainless steel or aluminum primaries in my steel tank? Wouldn’t that make for a longer-lasting primary shutoff?
Bill O’Roark
Little Rock, Ark.
ANSWER:
Let’s first discuss whether an aluminum or stainless steel primary can be installed into a steel tank. First, cross off the aluminum primary. Aluminum and carbon steel are not copasetic with each other. Aluminum cannot be welded to carbon steel. In recent years, they have been able to “fuse” aluminum to carbon steel, but most of that application has come from the space industry. And as you might imagine, it’s probably cost-prohibitive. So forget the aluminum primary.
Stainless steel and carbon steel can be welded together with no problems. The question is, does it make “cents” to replace a carbon steel primary with a stainless steel primary? In recent years, the price of both carbon and stainless steel has risen dramatically. Currently, stainless is approximately six times higher than carbon steel. It’s true that carbon steel primaries will rust over time and eventually they simply rot away. But, depending on your environment, some primaries have a reasonably long life.
Let’s assume a few things. Suppose over the life of your vacuum tank that your primary has to be replaced once or even twice. It still will be cheaper to replace the primary using carbon steel. Some primaries actually will last as long as the tank. A stainless steel primary will definitely last forever, but why do it, when even your tank will not last forever?
Our rule of thumb is to match carbon steel with carbon steel. What purpose is served if your stainless steel primary outlives your carbon steel tank? When you get ready to replace your tank you’re going to be giving up an expensive primary. On the other hand, if you’ve got more money than you need or want (and we don’t know many people in this boat) then go ahead and put the stainless steel primary in your tank.
A side note: The same rule holds true on your secondary moisture trap. Generally, the secondary is bolted to the side of the tank, so an aluminum or stainless model could be installed to replace a carbon steel unit. But why spend the extra money?
The other down side of mixing and matching metal parts is fairly obvious. When repairs are needed, and/or replacement parts, it will be easier on you and your repair shop knowing the materials involved.
Don’t mess with the gearbox ratio
QUESTION:
I recently bought a used vacuum truck and the former owner told me that the pump was driven by a 2:1 gearbox. What exactly does that mean? I don’t know much about what’s underneath the truck. Is that something I have to change? Rodney Latham
Tustin, Calif.
ANSWER:
No. Don’t change anything. The gearbox is installed on the truck to make sure the vacuum pump runs at the right speed. The gearbox is connected to the transmission and basically bumps up the rpms coming out of the transmission. For example, many vacuum pumps are designed to run at around 1,100 rpm. If the power coming off the transmission is turning at 550 rpm, then that rotation speed needs to be doubled when connected to the pump. With a 2:1 gearbox, the rpm going into the gearbox is 550 and the rpm going out of the gearbox would then be 1,100. This will properly run the pump.
Some of these gearboxes also change the angle of the drive by 90 degrees. That is, the power coming out of the transmission is connected to the gearbox, and then that power is shifted 90 degrees over to the pump. By way of information, there are also 1:1 gearboxes and 1 1/2:1 gearboxes.
Unless you develop problems, don’t fool with the gearbox.
