INDUSTRIAL HEATERS PRIOR TO 1999
(A, FIGURE 1)
Pressure switch PSH will shut down the heater in the event of abnormally high pressure due to blockage in the coil. Moreover, switch ∆PL will shut down the heater in the event of abnormally low differential pressure due to blockage, leakage or pump malfunction.

Switch J400-S156B (shown as PSH) contains a single pole double throw (SPDT) switch. Its normally-closed (NC) contacts should be set to open at a pressure of 5 psi lower than maximum pump output. Its normally-open (NO) contacts are not used on these heaters.

Switch J400K-S147B (shown as ∆PL in A, Figure 1) contains a single pole double throw (SPDT) switch. Its normally-open (NO) contacts should be set to close at a pressure of 25 psi. Its normally-closed (NC) contacts are not used on these heaters.

CONSTRUCTION HEATERS 1995 TO 2003
(B, FIGURE 1)
Pressure switch PSL will shut down the heater in the event of abnormally low pressure due to a clogged strainer or pump malfunction. However, it may not protect against low flow due to leakage or blockage in other parts of the system.

Switch J400-S156B (shown as PSL) is the same switch as in A, Figure 1. But here it is used to sense low pressure. On HCS (single line) heaters its NO contacts should be set to close at a pressure of 10 psi. On HC (manifold heaters) heaters its NO contacts should also be set to close at a pressure of 10 psi. Its NC contacts are not used on these heaters.

INDUSTRIAL HEATERS 1999 TO 2001
(C, FIGURE 1)
Switch ∆P will shut down the heater in the event of abnormally low flow through the heater coil due to pump malfunction or blockage or leakage anywhere in the system. The problem is the limitations of the switch, which should be replaced as previously noted.

INDUSTRIAL HEATERS 2002 TO PRESENT
AND CONSTRUCTION HEATERS 2003 TO PRESENT (D, FIGURE 1)

Switch ∆P will shut down the heater in the event of abnormally low flow through the heater coil due to pump malfunction or blockage or leakage anywhere in the system.

Please refer to Heatec Tec-Note, Publication No. 5-04-122 for information on setting Barksdale pressure differential switches now used on all Heatec thermal fluid heaters.