The dome-loaded BD4 regulator is the same build as our BD3, but includes a bottom return spring for proportional band control. This setup is used when closed-loop feedback is required, making it a perfect partner for our QBX electro-pneumatic regulator. The BD4 has a diaphragm for better response and/or more precise pressure or vacuum control than piston-type regulator. • Large CVs • Easy inline maintenance • Ideal for piloting by Proportion-Air electro-pneumatic regulators BD dome-loaded pressure regulators provide accurate pressure control of most industrial gases and liquids. All BD series valves are non-relieving. This series thrives in the oil & gas and petrochemical industries. These heavy-duty quality casted valves offer 1/2″ to 2” threaded ports and flange options from 1/2” to 8”.