Bulk Material Flow Control Gates (Part 2)
Posted on Thursday Apr 11, 2019 at 04:46PM in Belting & Conveyors
Mass Flow Gates
There are many reasons to store some bulk materials in storage silos that promote mass flow. If the discharge gate of a mass flow silo does not promote mass flow, mass flow will not occur in the storage silo. One of the most reliable methods of controlling the flow from a mass flow storage silo without disturbing the flow is a properly designed mass flow gate. Purvis Industries provides two types of standard mass flow gates.
Single Blade Mass Flow Gate
The single blade mass flow gate has one fixed inclined side that is not less than the calculated slope to promote mass flow for the product stored. The moveable blade when fully closed is the same slope as the fixed side. The other two sides are vertical. As the moveable blade is opened and closed the flow rate is changed but mass flow is always maintained. The center of discharge of the single blade mass flow gate changes by half the opening size but in most applications that produces no significant design challenges.
Purvis Industries’ standard single blade mass flow gate is produced in 48” square and 60” square sizes and fabricated of ¼” mild steel with 3/8” 400 BHN steel liner in wear areas. The movable blade is actuated by a hydraulic cylinder and mounted to a round shaft supported by flange bearings. The entire gate, including the moveable blade, is structurally reinforced and the entire unit is totally sealed.
Double Blade Mass Flow Gate
Two opposing sides of a double blade mass flow gate are moveable while the two other sides are vertical. When closed, the slope of the moveable blades is not less than the calculated mass flow angle of the material in storage. When discharging material, both blades move in unison to control the flow rate. Mass flow is therefore always assured while discharging on the gate center.
Purvis Industries’ standard double blade mass flow gate is produced in 48” square and 60” square sizes and fabricated of ¼” mild steel with 3/8” 400 BHN steel liner in wear areas. The blades are actuated by hydraulic cylinders and mounted to round shafts supported by flange bearings. The entire gate, including the moveable blades, is structurally reinforced and the entire unit is totally sealed.
Since mass flow gates are intended only to insure mass flow while controlling the material flow rate, it is necessary to install a shut off gate ahead of the mass flow gate. Purvis Industries recommends the double blade horizontal slide gate be installed on the inlet flange of a mass flow gate.
It is not possible to anticipate all types or sizes of gates that will be required. Some of the factors that determine gate sizes and arrangements are:
- The type and size of the material to be handled. If the flow of large material (+6” for example) is anticipated, it is important gates be provided that gate blades be designed in a manner that prevents the material from interfering with the closing of gate.
- If the material’s surface moisture is high, water can be expected to drain during storage. If the flow control gate is not designed to drain that water to a sump, a very dangerous situation can develop. Fluidized bulk material flowing freely in a confined space can endanger life and property.
- Should a flow control gate be required to be retrofitted in a confined space, the designer may be called on to use ingenuity to produce a design that will both perform the desired function and fit into the available space.
- Many other special conditions are often encountered to challenge the design capability of the gate designer.
Purvis Industries has the design and fabrication facilities required to produce the gate you need.
Gate Power and Control Systems
Purvis Industries is also uniquely capable of designing and supplying the actuating power units and complex control systems for all applications. Some operations depend on the flow control gates operating in a very complex and accurate manner. For example, loading railcars to gross weight without overloads at loading rates in excess of 16,000 TPH requires very exact blade positioning, timing, gate, acceleration, and velocity to meet governmental metrological requirements. The control system required to provide that operation includes computer and PLC programming that not only allows the goal to be achieved but allows it to be achieved in a manner that minimizes maintenance required by the operating equipment.