Solenoid Valve

Function

The solenoid valve translates a PLC digital output into a fast, repeatable flow-control action that starts or stops media delivery at precise points in the plant cycle. In the bitumen circuit, solenoid valves control individual tank outlet ports, temperature-sensing bypass loops, and the main supply to the spray bar; their response speed directly affects bitumen dosing repeatability and, therefore, binder content accuracy in the finished mix. In the burner fuel circuit, solenoids form part of the safety shutdown logic — a slow-closing or internally leaking fuel solenoid is a combustion-safety hazard and must be replaced immediately. In compressed-air circuits, solenoids control pneumatic actuators and purge sequences; a stuck-open air solenoid depletes the plant's compressed-air supply and disrupts pneumatic instruments across the whole system.

Construction & quality

Bitumen-duty bodies are in close-grained cast iron with integral electrical heat-jacket ports (½" BSP), externally lagged, rated for continuous service at up to 200 °C body temperature. Fuel oil and water duty bodies are in dezincification-resistant brass (DZR) or 316L stainless steel for corrosive media. Plunger, core tube, and spring are in austenitic 304 stainless steel, precision-ground to close diametral clearance for reliable actuation without sticking. Solenoid coils are copper-wound on a nylon former, encapsulated in Class H epoxy resin (rated for continuous energisation at 180 °C ambient coil temperature), and terminated to a DIN 43650A connector for standardised field wiring. Seat and seals in PTFE (bitumen), Viton/FKM (fuel oil), or NBR (water and air) depending on duty. Normally closed (NC) configuration is standard for safety applications; normally open (NO) available for bypass circuits. Manual override push-pin standard.

When to replace

• Valve fails to open or close on a confirmed PLC output command, with coil voltage verified at the connector
• Visible external leakage at body/bonnet joints or around the manual override stem
• Coil body noticeably hotter than ambient after normal duty — indicating coil resistance degradation or partial short
• Sluggish or slow actuation causing timing faults or alarms in the burner safety or bitumen sequencing logic
• Internal seat erosion confirmed by drip-through flow in the fully closed position at normal operating pressure