Cheaper for a reason

So, my pressure washer packed it in this past weekend.

My son was rinsing off the truck, and all of a sudden the pitch of the pump changed.  He released the trigger, and the pump didn't shut off like it normally does.

I killed the power, and discovered that the washer was spraying water out of the pump housing.

After we finished rinsing the car with the regular nozzle, I tore apart the pressure washer in search of the problem.

The photo is the pump assembly. In the foreground is the fitting where the soap tank attaches. If you look closely, you can see a seam in the plastic.

That seam is the problem.

The seam has failed, so the pump no longer works. This is apparently a common problem with this type of pressure washer. There is no fix that I'm aware of. (A replacement pump costs as much as a whole new unit.)

In hindsight, I'm not surprised. This unit was cheap, less than $150 CAD. Even though it has a good brand name attached to it, it's at the bottom end of the pricing scale for pressure washers.

What did surprise me was the time to failure; I've owned this unit for about two years. I expected even a cheap unit to last longer than that, considering the care I was putting into it.

I learned three things from this experience:

1. Buy a pressure washer with an all metal pump. They cost more, but last longer.
2. It's cheaper for a reason.
3. Cheap crap is crap and no amount of maintenance or TLC will change that. I made sure to purge the water every fall, and I stored the unit in the basement so there was no chance of freezing. That didn't stop it from failing.

OK, I kinda already knew the second one. But I've learned that a pressure washer is really worth two or three times what I paid for mine, and rather than throw good money after bad, I have to decide if I really need one.

Garage door

My radio hobby has been put on hold.

With the arrival of March comes the melting of snow, which means that I, and not the weather, am the factor holding up my spring projects.

First and foremost of those projects is fixing the garage door.

Now, before I go any further, I'm going to point out that this article is for entertainment purposes only. Garage doors are dangerous if installed improperly, and you can easily injure or kill yourself or someone else, or cause a lot of property damage. So I don't recommend that you attempt to install or adjust an overhead door. Now, back to our regularly scheduled programming.

Back in January the spring announced its retirement with a loud bang. Normally this wouldn't be a big problem, except that the door assembly came from Wayne Dalton, which means it uses their proprietary counterbalance system, and because my door is too old, I would have to shell out several hundred dollars for a complete counterbalance kit.

Fortunately, my father had recently replaced his garage door. New doors tend to come as a kit, which means you get not only the door, but also the track, pulleys, cables, springs, and various sundry hardware to install it. This means that after all was said and done, my father was in possession of a complete counterbalance kit which, although old, was still very serviceable. Modifying my door to use the old spring system seemed a much more cost-effective option.

It turns out that not much has changed in garage door technology in the past several decades.

First, a brief primer for anyone who doesn't know how an overhead door works.

To start with, they're heavy. Mine is about 55 kg, or about 125 lbs., which is too heavy for me to lift, nevermind the garage door opener (which doesn't actually lift the door, but I'll get into that later.)

In order to make the door usable, it's attached to a counterbalance that reduces the weight of the door by exerting an upward force on the door to reduce the net force required to lift it.

The problem with an overhead door like mine is that their weight changes as they move up and down. This is because as each segment rounds the corner on the track, that segment no longer pulls the door downward. What this means is that simply attaching a pulley and weight to the door won't work; as soon as the door starts to go up, it will go out of balance and shoot up because the counterweight will be too heavy.

The answer to this is to use a spring. The force a spring exerts is proportional to its spring constant, which is determined by its manufacture,  and the amount that it is deflected (pushed away from its resting position). So, as the door is raised, the spring's deflection is reduced, and the system stays more or less in balance through the entire travel of the door.

Fitting the old spring system to the new door turned out to be easier than I expected. (I won't go into the gory details here.) I had to replace a couple brackets to make room for the larger pulleys. I had to modify the cables that connect the door to the spring mechanism. And finally, I had to cut the shaft upon which everything mounts, as the donor door was 6 feet wider than mine.

Once all the hardware was mounted, it was time to load the spring. Here was the moment of truth; the donor door was much larger and heavier than mine. It was also about a foot shorter. All this means that the springs might not work for my door.

Remember that the force exerted by a spring depends on its spring constant and the amount it is deflected? Well, I knew from doing the math that I needed to twist the spring at least eight full turns in order for it to work; any fewer and it would stop exerting a force on the door before it was fully open, which would cause the cables to come off the pulleys and jam the door.

The problem was that if the spring was too stiff, it would overpower the door before I got to eight turns, and the door would open by itself.

Now, the donor door had two springs, which shared the lifting force equally. My plan was to use one, which cut the lifting force in half, and hope that the door would balance.

As it turns out, my hope was not in vain. Ideally, the door should be balanced at all points in its travel (ie., not want to go up or down on its own when stopped at various points.) Mine isn't quite so good; it's balanced at the bottom, but gets a little lighter near the top. However, it's close enough that it's not dangerous, and there's enough tension on the cables, even at the very top, that the door works.

It's not so far out of balance that it causes the garage door opener any stress, which is the most important thing.

Oh, right, the garage door opener. I said I was going to explain what I meant when I said that it doesn't lift the door. Well, it doesn't, at least not directly. Mine has a horizontal track that pulls the door away from the wall and the door follows. This only works because the opener is pulling at the very top of the door, where it is ready to follow the horizontal track along the ceiling. This means that the opener is not very well able to cope with an unbalanced door, as it's not able to directly oppose the force of gravity that's holding the door closed. And that is why a balanced door is so important; if the door were too heavy, the opener won't be able to open it. At best, the opener will stall and shut down. At worst, the opener could burn out, or it could tear the top of the door apart (although I would bet that most openers are both too smart and too weak for this to happen. But hey, why take the chance?)

So that's one major springtime project out of the way. My next task is to get the RV trailer ready for camping season, since our first outing is in less than two weeks. Stay tuned.