Modulating suction-side production system. Often imitated, but nothing else even comes close.
Automation package for Linear Cutters. Relentless pursuit of production.
Automatic booster pump inlet pressure control.
Automatic pipeline velocity control.
Plugged or nearly plugged pipeline?
Dredge pump cavitation?
Interruptions due to cave-ins?
The answer to the questions is a CONVAC system. More than just an emergency suction relief valve or suction bypass, the CONVAC system is a suction side production tool for hydraulic dredges. Instead of merely flying open to admit water into the suction in response to a setpoint, the CONVAC system has a “modulated” response. “Modulating” means that the system makes small corrections, and opens the bypass valve only as needed to maintain the desired production rate.
Introduced in 1993, the original CONVAC system revolutionized suction side controls for hydraulic dredges. 30 years later the CONVAC S4 with LNV continues the innovative tradition with improved controls, automatic Cavitation Killer and the LNV bypass valve.
Shown above is the CONVAC control panel and the LNV bypass valve assembly. The control panel includes displays for Vacuum, Velocity, Discharge Pressure and Bypass Position and becomes the primary operating instrument. The LNV bypass valve precisely meters the bypass water. Other CONVAC system components include a dedicated hydraulic system and a pump inlet pressure sensor.
Dredge operation without CONVAC
Dredge pump inlet pressure (vacuum) is the operator’s main source of information as to when and what should be done to maintain dredge production. Inlet pressure is an indicator of the density of the slurry that is flowing up the suction pipe to the pump inlet. With a constant pump speed the inlet pressure can be varied to maintain a constant velocity. When this occurs, the slurry density remains nearly constant in the suction pipe and solids production will be nearly constant. The operator’s task is to maneuver the suction inlet so that the inlet pressure is maintained as required to maintain production at the desired rate.
Slurry density is determined by the ratio of solids to water in the mixture flowing in the suction pipe. Moving the suction inlet changes the ratio by increasing or decreasing the amount of solids taken into the suction inlet. The desired production rate and velocity determines the correct amount of solids. The suction inlet is moved into the material bank to increase the amount of solids and moved away from the material bank to decrease the amount of solids. The operator must constantly monitor and adjust the inlet pressure to maintain the desired rate of production. If the operator does not make the correct adjustment the system will either overload and plug or production will be less than the desired rate.
If excess pumpable solids are available at the suction inlet the CONVAC does the major part of the operator’s task by automatically adjusting the amount of water entering the suction pipe.
Dredge operation with CONVAC
With CONVAC the operating goal remains the same – keeping the proper amount of solids coming into the suction. The difference is that the CONVAC will automatically regulate the solids to water ratio in the suction.
The operator inputs the maximum vacuum setpoint. The suction is maneuvered to create excess pumpable solids at the suction inlet and the vacuum reading increases to the setpoint. At this time the bypass valve opens only as much as required to prevent the vacuum reading from rising above the setpoint. The position of the bypass valve is indicated on the bypass valve position display.
The position display becomes the primary display to indicate when the excess solids are available at suction inlet. Ideally, excess solids will be available and the bypass valve will be “modulating” to control the vacuum. When this occurs there will be continuous production at the desired rate.
If a cave-in covers the suction inlet the bypass valve will open further to assure that adequate water is available to maintain system flow. If the cave-in does not stall the cutter the operator can leave the suction in the material and let the CONVAC adjust the solids to water ratio and maintain uninterrupted production. If the cutter is stalled the ladder need only be raised as required to unstall the cutter.
In addition to the vacuum setpoint, CONVAC also has a setpoint for low system velocity. If the system velocity drops below the setpoint the bypass valve will open until the system velocity rises. The low system velocity setpoint is a fail-safe feature to prevent pipeline plugging if the system becomes overloaded.
The CONVAC system takes the drudgery and stress out of dredge operation by continuously monitoring and maintaining the desired vacuum. Even the most attentive and caring operator cannot duplicate the relentless control of the CONVAC. The CONVAC system will pay for itself by increasing production and preventing pipeline plugging. Profits will rise when CONVAC controls the rate of solids intake.
Practice safe dredging, always use a CONVAC S4.