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.
Posted on Thursday Apr 04, 2019 at 05:25PM in Belting & Conveyors
Producing, processing, transporting, and using bulk materials requires gates to control the volume and direction of material flow. Purvis Industries can provide state of the art flow control gates of all different types. Purvis Industries’ standard gates are designed for bulk material of highly abrasive material with bulk densities of up to 120 PCF. This blog will describe several of the standard gate types we offer and briefly describe their operation and use.
Horizontal Slide Gates
- These gates may be single or double blade gates of standard or custom sizes. When closed these gates stop the flow of material and when open allow the material to flow freely. When required the gate position can be modulated to control the rate of material flow.
Horizontal slide gates consist of a gate frame, gate blade supports, blade support protection liners, blade support quick inspection and replacement equipment, gate blades, gate blade actuators, gate blade position indicators, one touch doors to facilitate access to the actuator to blade attachments, and unique hermetic seals. The standard gate actuators are hydraulic cylinders. Options are available for electrical, pneumatic, or manual actuation. Standard gate blades are made of 360 BHN steel plate lined with 7 ga. stainless steel. Gate blade supports are special UHMW blocks designed to minimize gate blade wear and gate maintenance.
Several options can be ordered with these gates. Blade position indicators, a very wide range of operational controls, dust tight seals of proprietary designs, high gate speeds, and precision gate blade position control are a few of the most requested options.
Standard sizes of single blade horizontal slide gates are 24” to 60” width and 24” to 60” stroke. Standard sizes of double blade horizontal slide gates are 24’ to 60” width and 48” to 60” stroke.
Rack and Pinion Gates
- These gates may be single or double blade gates of standard or custom sizes. When shut these gates stop the flow of material and when open allow the material to flow freely. The gate position can be adjusted to set the rate of material flow. The gate blades are made of 360 BHN steel plate lined with 7 ga. stainless steel plate. The blade supports may be specially designed UHMW blocks or cam followers.
- Rack and pinion gates are generally operated by a hand wheel or chain wheel attached to a gear reducer. The force required to open a gate is limited to not more than 50 lb.
- These gates consist of steel frames with perimeter openings into which round rods may be manually inserted. When all rods are inserted, material flow is shut off. This is sometimes done to facilitate maintenance downstream of the gate. Rods can also be inserted to control the flow of material through the gate.
- Standard rod gate sizes are 24” to 60” wide and 24” to 60” long.
- Diverter gates are used to direct material in the desired direction. Purvis Industries’ standard diverter gates are built of ¼” mild steel plate with 3/8” 400 BHN liners in wear areas. The gate blades are 3/8” mild steel plate welded to a round shaft supported as required by internal stiffeners. Blade liners are 3/8” 400 BHN steel plate. Standard outlets for the diverter gates will be 30 degrees or 0 degrees from vertical.
- Each gate blade will be equipped with a removable panel to facilitate blade removal for maintenance without having to remove the entire gate.
- The gates will be 18” square inlet with two or three 18” square outlets. Each blade shaft will be supported by two flange bearings bolted to the gate body. A torque arm will be attached to each shaft to transfer the torque to rotate the blade. The standard torque arm actuator will be a hydraulic cylinder. Alternate actuators may be electric, pneumatic, or manual.