Heatec currently uses Barksdale Dialmatic pressure switch CDPD2H-A80SS on all Heatec thermal fluid heaters.

Differential pressure refers to the difference in pressure at the inlet and outlet of the helical coil of the heater. Differential pressure is related to how fast thermal fluid is flowing through the coil.

It’s extremely important to maintain adequate flow to avoid damaging the heater coil, to prevent breakdown of thermal fluid and to achieve efficient use of the heat produced by the burner.

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. Moreover, a fire could result if there is leakage of thermal fluid inside the heater.

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.

How the differential switches work
The Barksdale unit has two pressure differential switches in limit circuits that shut down the burner when abnormal differential pressure across the heater coil is detected. (See Figures 1 and 4). It’s important to remember that both switches are differential switches. Both always sense the pressure difference between two points, the inlet of the heater coil and the outlet of the heater coil! One is normally open and is set for low pressure. The other is normally closed and is set for high pressure. Each opens or closes according to the differential pressure set on its dial.

Two pressure gauges are also used. One is on each side of the differential switch. One gauge always indicates the pressure at the inlet of the heater coil. The other always indicates the pressure at the outlet of the coil.

Do not confuse the pressure indications shown on these two gauges with coil differential pressure. Neither gauge alone indicates coil differential pressure. To determine coil differential pressure you must subtract the smaller pressure indication (value) from the larger indication (value).