By Ken Boyce
It’s important for pump buyers to understand their requirements for casing materials, port sizes, power options, features, maintenance needs and total cost of ownership prior to making a purchasing decision
The Ingersoll Rand Pit Boss air-operated diaphragm pump has a unique exhaust check valve to prevent water and contaminants from entering the air motor system, enabling it to function while fully submersed.
According to a recent Research and Markets report, the U.S. metals and mining industry grew by 5% to $201.5 billion between 2007 and 2011. Research and Markets anticipates even faster growth—around 6.3%—will drive the industry’s revenues to $273 billion by the end of 2016.
As the U.S. mining industry grows, so does the need for reliable dewatering solutions. Standing water is an issue for miners in most regions, and contractors rely on diaphragm pumps to clear the site before they send in employees and equipment. Most mining contractors bid projects on flat rates, and it is critical that the project remain on schedule to stay within budget. If a pump breaks down during the dewatering process, it causes production delays, which quickly drives up project costs.
Evaluating Diaphragm Pump Options
Diaphragm pumps are available in a variety of materials, port sizes and power options. When selecting a diaphragm pump for dewatering applications, buyers should look for features that increase its reliability and durability to help prevent breakdowns.
Diaphragm pumps’ casings are made from metallic or non-metallic materials, and some of the most common include aluminum, stainless steel and polypropylene. If mining customers are uncertain about the composition of the standing fluid, they should use a pump with an aluminum casing because it is corrosion-resistant and compatible with a wide range of fluids. In addition, aluminum is lightweight, which makes it easier to transport around the site and durable enough to withstand rock and sediment on location.
The pump’s design affects its flow rate and portability. Most diaphragm pumps are offered in 1-1/2-, 2- or 3-in. (38-, 50.8- and 76.2-mm) ports to handle moderate to heavy flow rates, which vary by application. It takes crews longer to clear standing water using the 1-1/2-in. port, but the pump is more compact and lightweight than the 3-in. model, to facilitate transportation. Diaphragm pumps designed with comfort-grip handles are easier to move—and more ergonomically friendly—than the pumps without handles, which require workers to lean over and grab the pump by the manifold.
Mine operators and contractors have the option to use air- or diesel-operated pumps. Air power pumps meet the stringent requirements of hazardous environments, where electrical or diesel-driven units are not considered suitable. If contractors are uncertain whether the standing water contains traces of diesel fuel or combustible substances, they should opt for an air-operated diaphragm pump, which meets applicable codes and grounding requirements.
Selecting Features that Increase Reliability
Buyers can choose from generalpurpose diaphragm pumps or dewatering pumps designed specifically for mining applications. Either option can be used to remove standing water from a pit, but dewatering pumps are specifically designed to prevent the most common pump issues, which include clogging, stalling, centering, tipping and air blow-by.
Most clogging issues occur when foreign particles get trapped in the pump during the dewatering process. If this occurs, the pump continues to cycle without pushing any water through the hose, causing production delays. When making a purchasing decision, it is important to select a pump with a removable screened inlet that prevents rocks and debris from entering the system and keeps it flowing smoothly. Removable screened inlets also give operators the flexibility to take off the filter and attach a suction hose to the inlet, instead of submersing the entire pump.
Stalling, centering and air blow-by commonly occur when operations use diaphragm pumps designed with balanced valves, which allow air to leak into the atmosphere, wasting energy and falsely inflating operating costs. Models with unbalanced valves are built with a large diameter on one end of the valve and a small diameter on the opposite end to create the optimal pressure difference. Since the valves are biased toward one side, they do not leak, center or stall the pump—even under low air inlet pressures. Unbalanced valve designs also produce a consistent material flow, which increases reliability and prevents unscheduled downtime.
Many diaphragm pumps stall when they are submersed in fluids. This can be prevented by using a pump that has a one-way exhaust check valve. The exhaust check valve prevents water—and other types of contamination—from entering the air motor system, and enables the pump to function while it is fully submersed. This feature gives customers the versatility to drop the pump directly into the pit, instead of setting up the pump on the surface level and dropping a tube into the hole to extract the standing water.
Often, workers are forced to set up the dewatering pump on rocky or uneven terrain in order to remove standing water from a pit. If the pump tips over before it starts running, it will not operate properly and may leave surface water behind. It is important to select a diaphragm pump with an integrated base plate to ensure it operates effectively on soggy and unstable terrain, which is common in the mining environment.
Routine maintenance is the key to keeping diaphragm pumps running reliably. The frequency of the maintenance schedule should be based on the performance of the product, instead of hours of operation or millions of cycles. It is time to perform routine maintenance activities if the pump displays any of the following behaviors:
• Reduced performance, which may indicate air leakage in the motor;
• Fluid leakage, which may indicate a ruptured diaphragm; or
• Reduced fluid output, which may indicate ball or seat deterioration caused by abrasive materials.
Pumps performing severe applications and/or moving abrasive materials require more maintenance than those used for general and non-abrasive applications. Choosing a pump with a lube-free motor also reduces the amount of maintenance required to keep it operating effectively.
Selecting Features that Increase Durability
Diaphragm pumps are put to the test in harsh mining environments. They have to be durable to withstand sediment and potentially abrasive fluids inherent in the dewatering application. Ingersoll Rand recommends contractors select a pump that can handle up to 1-in. (25-mm) particles to prevent stone, rocks or clay from clogging the system.
Over time, this sediment can create holes in the diaphragm pump as it moves through the system. If this occurs, contractors may notice fluid leaking from the manifold and reduced fluid discharge pressure. It is important to choose a pump with heavy-duty ball guides and manifolds that resist abrasive and semi-solid materials as they pass through the pump, to prevent leaks and extend the life of the product.
To help prevent leaks, customers should use diaphragm pumps with bolted, instead of banded, fluid caps. These models use a bolt to squeeze the air and fluid caps to the diaphragm, which creates an even clamping surface and a barrier to prevent leaks. Banded-design pumps use a clamp to hold the air and fluid caps to the diaphragm. The band degrades over time, allowing potentially harmful fluid to leak into the work environment.
Choosing the Right Pump for the Application
Given the number of diaphragm pump options in the market, it is important for end users to evaluate their requirements for casing materials, port sizes, power options, features, maintenance needs and total cost of ownership prior to making a purchasing decision. Ingersoll Rand recommends air-operated diaphragm pumps with aluminum casing, a removable screened filter and one-way exhaust check valve for mining applications. An interactive pump selector guide is available at ingersollrandproducts.com/am-en/products/fluid/aro-pump-selector to help customers select the right pump for their next mining project.
Boyce ([email protected]) is product manager of the ARO diaphragm pump portfolio at Ingersoll Rand.