A single bleed valve, plugged, capped, blinded, or piped to a safe location when specified, should be provided for all required applications (Plugging, capping, blinding, or piped to a safe location is required for personnel protection). Bleed valves should be NPS 3/4 minimum and should have threaded outlets. Bleed valves should be located as follows:
- Bleed valve is required to safely depressure the system, check for leakage, and/or direct leakage to closed drain system.
- For pressure relieving (PR) devices, Bleed valve is required to safely depressure the system, check for leakage, and/or direct leakage to closed drain system:
- Between the PR device and the inlet block valve.
- Between the PR device and the outlet block valve unless the PR device discharges to atmosphere.
- For all shell-and-tube and double pipe heat exchangers, when a manually operated bleeder valve is used for overpressure protection against liquid thermal expansion, the valve should be installed on the cooler side.
- When a body bleed is required, the bleed valve should be located on the block valve body or bonnet (for gate valves: position G, H, I, J, or K per ASME B16.34, Figure 1) for valves NPS 3 (75 mm) and larger. Where it is not feasible to provide a bleed (due to size or other constraints), two block valves with an intervening bleeder should be provided.
- Between the block valve and the associated equipment item for all onstream equipment isolation applications, a drain valve already specified in this location, and not piped to a closed drain system, is sufficient to meet this requirement.
- Between the block valve and isolation blind for onstream isolation of equipment in dangerous material services, unless the block valve is equipped with a body bleed in position C or D on the blinding side of the valve, defines alternative bleed valve location to safely depressure the system, check for leakage, and/or direct leakage to closed drain system.
- Bleed valves are not required for:
- Single and double block valves at instrument takeoff connections.
- Double block at vents, drains, flushing, and cleaning connections.
- Where PR devices are installed for thermal liquid expansion protection.