Spray Bar Section Valve

Function

When a section valve closes, it simultaneously shuts off bitumen supply to its nozzle group and, in balanced-port designs, equalises residual line pressure to prevent post-close drip. Fast closing response — under 0.5 seconds at rated actuation pressure — is critical on surface-dressing runs at 3–8 km/h; a slow or leaking valve produces a ragged spray edge, wasting binder and requiring additional edge rework. Positive shutoff also prevents the bar from flooding when the machine is stationary on a grade.

Construction & quality

Body: ductile cast iron or carbon steel, epoxy-powder coated internally and externally for bitumen service. Seat and ball or plug: hardened stainless steel (440C or equivalent), lapped to metal-to-metal seal. Actuator: double-acting pneumatic cylinder rated for 4–6 bar air supply, or hydraulic up to 25 bar, with stainless steel rod and PTFE-lined cylinder bore. Spring-return failsafe-closed option is available. Stem seal: live-loaded PTFE chevron packing. Body rated PN16.

When to replace

• Bitumen seep past the valve body at section joints when valve is commanded closed
• Slow actuation response or failure to reach fully open or fully closed position
• Air or hydraulic supply bleeds down faster than normal — internal piston seal wear
• Valve stem becomes stiff or binds — carbonised bitumen build-up inside body
• Ragged or feathered spray edge during a run despite correct pump pressure