Heatec has used a variety of pressure switches in helical coil heaters to determine flow of thermal fluid. The switches are in limit circuits that shut down the heater when abnormal flow is detected.

It’s extremely important to maintain adequqate flow to avoid damaging the heater coil, to prevent breakdown of the thermal fluid and to achieve efficient use of the heat produced by the burner. Worse yet, a fire could result if there is leakage of thermal fluid inside the heater.

Abnormally low flow can result either from blockage in the thermal fluid circuit or from leakage due to a rupture in the coil or piping, or from a pump malfunction, etc.

Blockage is the most common problem. It is usually due to a strainer clogged by debris that the thermal fluid has picked up from the piping. This is more apt to happen upon the initial startup of the heater when there is debris left over from the manufacturing process and installation of the piping.

HISTORY
Figure 1 shows a history of what switches we have used and when we started using them. Early construction heaters had no pressure switches and are not pictured in Figure 1. We have improved our heater controls over the years. We have also made changes to meet insurance codes.

For a brief period we used certain types of pressure switches that proved to be unsatisfactory for use on Heatec heaters. The switches were made by Mid-West instruments and are shown in the accompaning photo. Their reed switches cannot handle the current in limit circuits of some of our heaters. As a result the contacts may fail, providing no protection against abnormal flow. Moreover, high oil temperatures may cause leakage in their internal sensing parts.

HOW EACH SYSTEM WORKS
It’s important to understand the protection offered by each system, past and present, and its limitations.

Heaters with no pressure switches have no protection against abnormal flow of thermal fluid. Thus, the heater will not shut down automatically in the event of blockage, leakage or pump failure.