Loading, unloading, conveying, or transferring bulk material often requires a temporary stoppage of flow or a containment of residual material. Choosing the right valve for the application depends on the requirements of the process, material characteristics, and potential for no-flow or static columns of material. These valve selection elements, combined with the cost of the valve selected will help determine the one best suited for each unique application.
A commonly used valve in bulk material handling is an Iris valve. Typically the valve’s function is to “gently control the discharge of free flowing powders, granules, and pellets including chemicals, food and dairy, pharmaceuticals, minerals, and plastics in gravity flow applications” (How Does an Iris Valve Work, Vortex, 2016). Using this description and applying it to various aspects of a bulk material handling system identifies an Iris valve will work well on the discharge of a Bulk Bag Unloader. The Iris valve allows and operator to untie a bag and meter the discharge, it also allows for the bag to be closed off and retied during material flow or when the bag is empty. In each of these cases material loss and dusting are kept to a minimum. There are three common handle options for closure of the valve, see the image below.
The other valve option specifically for a Bulk Bag Unloader application is a pinch valve, shown below. This valve has pneumatically operated plates which are designed to close in a static material column. These valves are more expensive than an Iris valve however, offer the ability to close off a material section in the event a hopper is full or there is a material back up within the system for any reason.