Electric or diesel? Any decisions should take into account critical factors such as required volume, flow/head specifications and the constitution of water and materials to be pumped. Pump capability has to encompass the variables of operational conditions, site access, project duration, environmental issues, equipment autonomy and much more.
Here are five key considerations you should focus on when you choose to buy or rent a diesel or electric pump:
Power and Flow
Sturdily built for endurance and reliability, diesel powered centrifugal pumps are designed for handling high volumes of water discharge. The operating flow range is typically between 50 to 830 m3h with a head of up to 51 metres. In addition, these pumps are able to operate in a high variable speed range, which enables them to cover different applications and flow/head combinations.
By comparison, medium-to-large electric submersible pumps offer maximum power ratings in the region of 54 kW and can typically manage flows from 225 to 16.500 litres per minute with a maximum head of 85 metres.
These are the typical range; however, some higher-head pumps are available.
Diesel driven centrifugal pumps can work with water that is clean or dirty as well as handle trash and fibrous materials. Their solids handling capacity can reach up to 76 mm in size thanks to features such as semi open impellers and abrasion-resistant pump casings. Discharge connection diameters typically range from 75 – 200 mm.
In contrast, electric submersible pumps have the ability to handle abrasive materials and solids up to 12 mm (higher with sludge pumps), although it’s highly recommended to equip them with hardened impellers when handling suspended solid.
Electric submersible dewatering pumps offer portability, easy handling and are generally available in a power rating and capacity range that make them well suited to ground water control applications; including emergency duties. For instance, construction and mining sites where a pump with a small footprint is needed, such as when draining a sediment tank. They are also useful for applications where diesel pumps cannot be used, for example underground mining or where emissions are not allowed.
On the other hand, fully automatic self-priming diesel centrifugal pumps are the de facto choice for delivering fast dewatering solutions to sites where an alternative power source, such as a generator or mains feed, is not available. They are the ideal solution for transporting or raising water with large abrasive solids in suspension; such as in construction and mine site dewatering, floodwater, stream diversions and municipal applications. Transportation and storage handling at remote sites is simplified if these pump units feature forklift slots and a built-in lifting eye.
Providing hours, and even days, of unattended dewatering pump operation, submersible pumps can meet the demanding requirements of raising water from great depths or lowering water tables even in the toughest environments; with some models capable of running for up to 2,000 hours without attendance. As they are sub-surface units they can continue working under ice in freezing conditions; as long as the pump is completely submerged. Where appropriate to the task, electric pumps offer environmental compatibility. For instance, quiet running is an essential feature of their performance when they are sited in populated areas or employed in night-time operations.
When equipped with a reliable engine and high capacity cooler, centrifugal pumps will ensure continuous and safe running even at high ambient conditions. Together with fuel autonomy of around 40 hours, continuous drainage is made possible even with significant volumes of air (snore conditions) thanks to an oil-free diaphragm vacuum pump’s automatic priming. In addition, some pumps can be equipped with an extra large fuel tank that allows them to run for longer periods without refuelling.
Maintenance and service
With electric submersible pumps extreme durability is guaranteed as they offer high-wear resistance. Meanwhile, the modular construction of these types of pump provides for simplified maintenance procedures. Some models can also be equipped with on-site servicing and parts replacement kits, including seals and impellers.
With the exception of replacing wear parts and engine filters, maintaining centrifugal pumps is easy and simple. Another part of this type of equipment’s appeal to rental organisations is the inclusion of advanced controllers with data monitoring capabilities that flag up when service interventions are required.
It all comes down to the nature of the application and questions such as where is the site, how deep is the access point, what is the nature of the water/material mix to be pumped and how long will the equipment need to run to complete the operation?
Making the correct pump selection will depend upon the physical parameters – the static head height, the required hose length and its diameter. It will need interpretation of equipment manufacturers published flow rate v head height performance curves to find the BEP (Best Efficiency Point), and thus the pump best rated to deliver this performance. What’s more, there are also considerations to be made of friction losses and cavitation issues. So, overall, making the right choice is not a simple issue but with expert guidance from equipment suppliers or renters it can be achieved satisfactorily.