One of the big issues with any pumping or dredging application is the clogging of the pipeline or hose. Clogging most often happens due to large objects getting stuck or slurry settling in the pipeline and or hose. In order to minimize this issue, it is very important to choose the proper pipeline and size, along with the type of pump with the correct power.
Based on what slurry you are pumping, it is important to make sure that your pipeline, hose size, and type are correctly sized for your pump. This will make sure the critical line velocity maintains a high enough level where the material will not settle in the pipeline or hose and the accumulation will eventually lead to clogging. The critical line velocity is the velocity in feet per second that the slurry must travel through the pipeline or hose to remain turbulent enough not to settle at the bottom of the hose. The smaller the inner diameter is of the hose or pipeline, the higher the velocity of the slurry.
Critical Line Velocity Chart Below for common slurries:
|Solids Type||Solids Size (Mesh #)||Critical Line Velocity (ft/s)|
|Fine||200 or over||7-9|
|Sand||200 to 35||9-11|
In dredging applications when you are done dredging for more than 10 or so minutes it is extremely important to lift up the pump suction and pump only water through the pipeline until that is all you see out of the discharge pipe. This process will remove the accumulated material stuck in the pipeline or hoses. Skipping this step could cause the material to then dry up and settle in the pipeline or hose and potentially cause clogging.
Choosing a Discharge Hose
In dredging applications, it is common practice to use a high pressure (150 psi) rubber-lined corrugated slurry discharge hose that runs from the pump discharge a minimum of 50-ft and then connects to the pipeline. This type of hose is used because it is more flexible than rigid plastic pipeline and allows for a more versatile pump and dredging operations. The size of the slurry discharge hose is most often the size of the pump because the inner diameter is the same. For example, with a 6-inch pump, you would use a 6-inch slurry hose.
Choosing a Suction Hose
For suction hoses in diver operated pumping applications or self-priming pump applications, it is ideal to use a heavy-duty polyurethane lined material handling hose. This heavy duty is hose is corrugated and very flexible for these applications and built with tough, durable materials to withstand the high amount of abrasives commonly encountered while dredging. The size of the suction hose is usually 1-inch larger than the pump size. For example, a 4-inch pump would use a 5-inch suction hose.
For dredging or pumping slurry, It is best practice to use HDPE (High-Density Polyethylene) pipes, which is a hard plastic black pipeline. The size of the pipeline is usually 2-inch larger than the pump size. For example, if you are using a 6-inch pump, you would need 8-inch HDPE DR-11 pipeline which has an inner diameter of about 6-inch.
If pumping material short distances, you can also discharge directly from the flex hose. However, keep in mind that flex hose is more expensive than HDPE pipelines. For this reason, most setups utilize HDPE pipes to save on the initial cost of building the discharge pipelines unless the pumping distance is short enough for it not to matter.
Warning: Do not change discharge pipeline size out in the field!
The pump system designer or engineer needs to know if there is an existing discharge pipeline at the job site. If an existing pipeline is present and it will be used for the project, the pump system should be chosen to match the available pipeline. If pipeline needs to get changed in the field, the system engineer needs to know because this will change the entire dynamics of the pumping operation. Fitting a larger pipeline than necessary could cause the discharge to slow to a point that material begins to build up at the bottom of the pipeline, leading to clogs.
Pump Screen Attachments
If your pipeline or hoses are being clogged by large rocks or other large sized material, sometimes a screen attached to the pump at different stages will help. There are several methods to do this. One method is to attach a basket screen, along with a cutterhead attachment, to the end of the pump.
This combination can then be mounted on an excavator, barge, or ladder dredge to facilitate breaking up large chunks into smaller, more manageable pieces that won’t clog your pipeline. Including a basket screen with the cutterhead will ensure the solids you’re pumping are a certain size before being drawn into the suction hose.
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