Practical Automation for Hydraulic Dredges

Using our 25 years experience building dredges, and over 30,000 hours operating dredges, we have blended the technologies of the Programmable Logic Controller, [PLC], and electro-hydraulic proportional valves to develop the Production Optimizer System.  These technologies are used to control millions of machines in manufacturing, mobile, and marine equipment.  This article will explain the Suction Relief Valve and the Swing Winch Control, which are the main components of the Production Optimizer System.

A dredge pump will develop whatever vacuum is required to keep its case full of slurry, up to the cavitation point of 24 to 25 inches of mercury.  Suction vacuum is the key to optimizing production.  If the material will pass through the cutterhead to the suction mouth, then, the higher the vacuum, the higher the production.  However, when running a high vacuum, the discharge pipeline velocity must be high enough to prevent the material from settling and causing a pipeline plug.

   Suction Relief Valve: The Suction Relief Valve permits the dredge to pull a high vacuum without fear that the pipeline will plug.  Transducers sense the vacuum and pipeline velocity and send signals to a PLC.  Vacuum range and velocity range settings in the PLC, control the opening of a gate valve that permits dilution water to enter near the suction mouth.  If vacuum is above the high setting, or velocity is below the acceptable flow setting, a pipeline plug is eminent.    High vacuum or low flow causes the valve to open and dilution water enters the suction pipe near the cutterhead. The dilution water lowers the vacuum and raises the discharge velocity. 
Settings in the PLC permit the valve to be opened in 1 inch to 12 inch increments. A timer permits the valve to open a set distance, and then wait from 0 to 60 seconds to determine the reaction of the pipeline velocity before the valve is opened or closed further.  In the event of a bank cave-in, the emergency open feature causes the valve to open 12 inches in 3 seconds. Click here to see the Suction Relief valve.

   Swing Winch Control: Used on dredges that swing [move] during normal operation.  Automatically controls the swing speed.  This system senses the vacuum and adjusts the swing winch speed to maintain the vacuum within a set range.  To optimize production, the vacuum range is set slightly below the dredge pump cavitation point.  On a sand and gravel mining dredge, the vacuum range can be set at any range needed to match the production from the dredge to the capacity of the gradation plant. 

A ramp setting in the PLC controls the rate of speed change.  This smoothes the operation and prevents the system from hunting.  A manual speed control is also provided.  Adjustable tension is maintained on both swing winch cables.  On dredges that work on a 3 cable system, tension on both cables must be maintained to hold the dredge forward into the material.  If tension is not maintained on both swing cables, the dredge slides back away from the bank of material and all production is lost.

The formula for high production is: Swing speed controls vacuum, vacuum controls production and pipeline velocity, proper vacuum prevents pipeline plugging.  In the event of a bank cave-in, the Suction Relief Valve opens and prevents pipeline plugging.

Click here to see the Swing Winch Control.

   Ladder Control: Used on sand and gravel mining dredges that have a chain ladder.  This system senses vacuum and automatically controls the ladder winch to maintain vacuum in the most productive range.  Lowers the ladder if vacuum is too low, holds the ladder if vacuum is in the best production range, raises the ladder if vacuum is too high.  A simple, inexpensive, fast hoist option can be installed to double the ladder hoist speed in the event of a bank cave-in.  Ladder control assures optimum production and prevents pipeline plugging.

   Operator Control:  Operator control of the Production Optimizer System is provided by a color touch screen.  The touch screen shows the dredges vacuum, discharge pipeline velocity, and the position of the Suction Relief Valve.  Touch buttons permit manually operating the Suction Relief Valve, changing all the settings, testing the system and troubleshooting.  Operator control of the swing winches is by toggle switches with a rotary potentiometer [rheostat] for swing winch speed control when in the manual mode.  To see the touch screen, click here.

   Dredge Position Control: On dredges that use a 3 cable positioning system, it is important to know the distance that the dredge moves forward for each cut as well as the distance that the dredge needs to move back for clean up.  Our exclusive Wind-In / Wind-Out Encoder provided the distance that the dredge is moved for and aft.  To see the Encoder click here.

   The Production Optimizer System automates only the functions that benefit from automation and leaves functions that are best controlled by the operator, for the operator to control.

   The Production Optimizer System can be installed on new or existing dredges. 

   On a recent installation, the Production Optimizer System increased the production of a sand and gravel dredge by 50%. 

   The Production Optimizer System is an exclusive product of Dredging Specialists.

To see more tools in the Dredgers Tool Box click here.