Section H

Thermostats are pneumatic pilots designed to monitor and control temperature ranging from -30°F to 750°F Section H separable sockets increase working pressure from 500 to 7,000 psig T-12 Temperature Controller

Section H Base Assemblies [H: ] Snap Action Thermostats [H: ] Throttle Action Thermostats [H: ] “TC” Temperature Controller [H: ] High or Low Temperature Shut-Down [H: ] High Temperature Pilot Guard [H: ]

Thermostat on Heater Treater

Thermostats on Line Heater

T12

Separable Socket – Thermowell

indirect direct Indirect and Direct Thermostats

Indirect Thermostat T12 Negative feedback for linear output 5 to 30 psi air or gas supply pressure Stainless steel housing Bi-metal sensing element for accurate control Output pressure proportionate to temperature at any setting Single adjustment over Wide temperature range: T to 400 o F HT to 700 o F

Direct or Indirect Direct Mode Indirect Mode Rising Temperature Rising Output Falling Output DirectIndirect

Indirect Thermostat Indirect

Direct Acting Thermostat T 12DA Supply Output Direct

T12 DA Thermostat Output Supply Indirect Reversed for Indirect Throttle Mode

High Temperature Thermostat HT 12 Output Supply Indirect

Direct Snap Thermostat T 12S Output Supply Direct

Indirect Snap Thermostat T 12DAS Output Supply Indirect

Indirect Throttle Thermostat T 12T Output Supply Indirect

Direct Throttle Thermostat T 12TDA Output Supply Direct

Direct Semi-Throttle Thermostat T 12DAT Output Supply Direct

Indirect High Temperature Shutdown T 12M Output Supply Indirect

Direct Low Temperature Shut-Down T 12DAM Output Supply Direct

High Temperature Pilot Guard HT 12PG Output Supply Direct

Typical Burner Control Installation High temperature shutdown thermostat Burner control thermostat Safety shutdown valve Burner valve Main burner Pilot Pilot Guard thermostat Instrument Gas Low liquid shutdown pilot

Trouble Shooting SYMPTOM CAUSE Erratic temperature changes Continuous venting Bent sensing element (element should be centered in base and should “ring”) Incomplete immersion of probe Dirty pilot plug seat Hole in diaphragm Weak pilot plug spring Faulty ‘O’ ring

Trouble Shooting To check small seat: increase temperature setting several degrees and see if venting stops. To check large seat: decrease temperature setting several degrees and see if venting stops. Replace pilot plug and seats if unable to stop venting by cleaning seats.