There are a number of ways to exploit physics for our benefit. We take advantage of physics to make air conditioners, make friction-free braking electrical cars, and apparently make a valve without any mechanical actuation. That is, a valve we don’t actually open or close from the outside, it opens itself. In this case, it’s the valve component of a steam trap.
Everything changes at least a bit with temperature. Water tends to expand when it’s frozen, leading to burst pipes in the winter. Metals tend to stretch when they’re heated. This is something famously demonstrated by the Air Force’s SR-71 Blackbird, the engines were a massive four foot, eight inches wide and nearly eighteen feet long on the ground, during operation they would expand by six inches from the heat.
This type of expansion is commonly used in older, bi-metal thermostats. As the temperature changes, two pieces of metal change in size. This is something incredibly precise, allowing a basic thermostat to operate without any active components. It would always actuate based on temperature and nothing would change that. If it works in thermostats, why not use it in other places?
If we know an element will expand or contract at a given temperature or range, then we can make use that to perform a mechanical job. We put one of these elements inside a steam trap, when it’s expanded, the condensate drain is sealed by our temperature sensitive element. When the temperature cools, our material contracts and the valve component is essentially opened.
This is essentially a naturally regulated trap. Once it’s put together, it’ll either always actuate at the temperature it was built to work at or it’s broken. There’s no risk of a programming error in some controller or a worker mistakenly leaving a manually controlled trap open. It’s all self-contained and isolated from outside interference.
What’s The Point?
Traps like this are almost flying in the face of what we use a trap for. In most applications, we want to remove condensate immediately, don’t we? Condensation lags down our heating systems! It causes inefficiency! And while that’s true in your office building, there are industrial processes where it’s a different story.
The biggest example for a Temperature Trap is use in tracer lines. These are pipes, usually outdoor pipes where their fluid needs to be kept warm. This could be everything from the lines carrying processed gas across the country to transferring chemical products between buildings. Some compounds need to be kept within a specific temperature range. Oil needs to be kept warm to prevent it turning to a near impossible to transport sludge, chemical products, even drugs in production may need to be kept above a given temperature to avoid chemical breakdown or unwanted reactions.
In these situations, steam may be too hot and risks ‘burning’ the substance we’re heating. At the same time, we have vast expanses of ground to cover and heating water isn’t enough. The water would’ve cooled down before it’s run the length of the pipe. Steam becomes the only viable transport mechanism, it can be heated sufficiently that it provides hot, liquid water to the entire pipeline. When the steam condenses, it flows down and pools in piping inside or under our main material pipe.
This doesn’t resolve the need for a trap. There will still be unwanted, cold water present. Luckily, water follows the same physics as the air: hot water rises, cold water falls. The water at the higher points in the pipes will be the hottest water, so long as no significant mixing force is present.
At the lowest point on our tracer pipe, we put in the steam traps. These are all designed to open at the lower threshold of our desired temperature. Trying to maintain 50 degrees? The trap actuates when the water inside it is 49 degrees. The faster we get that cooler water out of the system, the more efficiently it operates.
Where’s the Problem?
There’s always another shoe that has to drop, isn’t there? There are a few flaws to these traps. They’re pretty much useless outside of industrial applications. This design would decimate a heating system’s efficiency. The traps themselves cannot be altered after installation. If your facility processes multiple materials in the same pipe and each needs a different set temperature range, these traps won’t work. You’d have to rebuild the traps for each temperature range.
Despite the near fool-proof actuation system, these aren’t fool proof either. We’re relying on a compound that’s going to change it’s dimensions with temperature. Whenever you heat and cool something, you expose it to fatigue. Metal eventually wears out, develops cracks and other flaws as it changes temperature. This is a slow process, but it can cause temperature traps to have a shorter life span than their mechanical counterparts. Other metals are unaffected by the temperatures involved in these traps. It becomes a trade off of whether you’ll maintain a control infrastructure and a maintenance infrastructure or just focus on maintenance of these traps.