Product Details: Equip your hydraulic system with vital replacement so you can be Ready for the Road Ahead™, with the Williams Controls WM147F Series Normally Open Relay Valve. With an open, non-compensating design, this hydraulic component is the ideal option to regulate excess air pressure. Manufactured with OEM standards and quality materials for use with idle and active heavy duty machinery. FleetPride is your First Click in Heavy Duty®.