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Screw compressors serve as key equipment in dry bulk transport

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Dry Bulk,

The new Euro 6 truck regulations have placed strict size and weight limits on transport vehicles, which serve as the lifeblood of the dry bulk transport industry. However, truck manufacturers still want to maintain the same product-transport payload capacities, which becomes problematic now that size and weight are in the crosshairs.

To meet these regulations, which also help transport trucks improve their efficiency, manufacturers are designing lighter vehicles and trailers. These new dimensions and lighter tractor-trailers, however, do not come without sacrifice. Because truck manufacturers still want to move as much product as possible, space becomes a premium commodity, which puts a critical eye on transport equipment. Unfortunately, most transport equipment is not known for being compact.

Yet there is one piece of equipment that can play a key role in helping truck manufacturers not only meet these new regulations but also provide efficient power in a small footprint. Screw compressors have those attributes and work well in bulk transport applications, regardless of the product being transferred.

This article will discuss why screw compressors are an ideal choice for transport vehicles in the bulk transport industry.

Screw compressor MX12.

The screw compressor principle

The composition of screw compressors is relatively simple. The male and female screw mesh and rotate in opposite directions inside the casing fitted with inlet and discharge ports.

Rotation generates a volume increase on the inner face between threads and grooves – which corresponds to inlet – and a volume reduction on the upper face, which corresponds to compression.

On the discharge port side, a set of gears synchronises the male and female screw, ensuring that they are not in contact. The discharged air does not enter in contact with any friction part and remains clean and free from particles.

On the drive shaft side, a set of step-up gears drives the female screw. An oil pump delivers pressurised oil, which circulates lubricating gears and ball bearings. Sealing is provided between lubricated parts and the compression stage utilising labyrinth seals. These seals do not come in contact with the shaft and are not subject to wear.

How they fit into the picture

At first glance, it appears that bulk transport trucks have an abundance of space for not only product but also a variety of different equipment. When you tally it up, however, the limitations become apparent. Transport trucks come in a variety of wheel configurations, including 4 × 2, 6 × 2, 6 × 4, and 6 × 6. From there, each vehicle carries several necessary accessories, including retarders, boxes, and a spare wheel. With the Euro 6 regulations, additional accessories are also required, such as a blue tank and catalytic muffler inside the vehicle’s frame. Add all of these accessories up and there seems to be limited, if not any space for a screw compressor.

Space does exist, however, it just means that the screw compressor must be compact. To make use of that limited space, Mouvex designed a screw compressor with a small footprint, known as the MX12 screw compressor. It measures between 21.3 - 22.4 in. (541 - 569 mm) long, 13.6 in. (346 mm) wide and 17.76 in. (451 mm) tall. That footprint allows the MX12 and similar screw compressors to fit on nearly all vehicle chassis without sacrificing space for other equipment or, most important, bulk product. A compact footprint also means less weight, which bodes well for these applications because the screw compressor will not reduce the vehicle’s fuel efficiency. The MX12 weighs only 242 lb (110 kg).

Designed to adapt

Bulk transport truck manufacturers do not know what the future holds, but that should not stop them from anticipating it and outfitting their vehicles with adaptable equipment. Screw compressors will work well with current and potential regulations if they have a modular design.

This design approach, found on the MX12, gives truck manufacturers flexibility when incorporating it into their vehicles. A modular design means these manufacturers can place it in a variety of different locations, especially if the compressor has numerous mounting configurations, a feature of the MX12. These kinds of compressors also give manufacturers the capability to repair them quickly if needed or make modifications or upgrades.

Designed to perform

A compact, modular screw compressor will fit on a bulk transport vehicle, but that ability does not do much if the actual equipment cannot adequately perform. Fortunately, a compact screw compressor does not have to trade away its performance to ensure a proper fit.

Naturally, screw compressors in bulk transport applications need to provide consistent, reliable performance to help offload a variety of bulk products, ranging from gravel and sand to cement and flour.

The imperative attributes for these applications include a reliable and fast flowrate, consistent pressure, and a low inlet speed. Flowrates up to 4975 gal./min. (1130 m3/hr) will give transport operators plenty of flow to cut the time it takes to offload a bulk product.

For example, this flowrate, one made possible from the MX12, can offload a standard bulk load within 30 - 50 min. An average screw compressor without that strong of a flowrate will complete that same job in an hour or possibly longer. While the size of the payload is important, saving time for additional payloads can improve the bottom line of any operation.

Another feature that should be paired with a fast flowrate is robust air pressure. Having enough air pressure ensures the integrity of the product being transferred. A good pressure benchmark for screw compressors in these applications is 29 psi (2 bar). This amount of pressure will give operators the ability to handle bulk loads of all sizes and consistencies.

With a fast flowrate and robust pressure achieved, the other essential attribute for a screw compressor in these applications is low inlet speed. Having this will benefit fuel costs and consumption, keeping both of them low.

Addressing common challenges

While every piece of equipment in bulk transport applications has its downsides, screw compressors have safeguards that address common challenges. For example, vibration is a detriment to compressors, yet they produce it just by operating. To combat this, one solution is mounting brackets or clamps to reduce vibration, yet over time it will still damage the compressor. A better way is to design a screw compressor with anti-vibration properties. With this built-in protection, vibration becomes less troublesome, which reduces downtime and increases equipment longevity.

Another common concern with screw compressors is overheating, which causes this equipment to stall and ruin the offloading procedure. Adding an oil radiator solves this issue because it regulates the screw compressor’s internal temperature. This feature prevents overheating, making the equipment unlikely to stall.

Screw compressors use a male and female screw mesh to achieve compression.

Screw compressor versatility

Screw compressors function well in bulk transport applications because they are versatile pieces of equipment. Even when exposed to challenging products or environments, screw compressors can be designed and outfitted to counter most detriments.

For example, when it comes to dealing with construction materials, such as cement, an integrated PTO module will ensure that the screw compressor will be compatible with most European truck frames. This means that there will not be a need for torque limiters, gimbals, or holders.

When dealing with dry bulk applications with extremely low atmospheric temperatures (-22°F [-30°C]), screw compressors can be constructed from hardened steel or cast iron, allowing for proper functionality and great material compatibility.

If space is even more restricted than typical standards, manufacturers can design screw compressors with footprints as small as 22 × 14 × 11 in. (549 × 348 × 280 mm) with a weight as low as 207 lb (94 kg).

When transporting and unloading liquid cargo, screw compressors should be outfitted with protectants. This includes stainless steel exterior components and protection on the compressor body and screws, allowing the equipment to better handle a wider range of chemicals. These safeguards also make abrasions and corrosion less likely.

Real-world example

Discussing the capabilities of screw compressors in bulk transport applications reveals their value to this industry. To further emphasise how important they are to an evolving industry with new regulations, Mouvex provided Lomas Distribution, one of Western Europe’s largest privately-owned hauling companies, with an MX12 screw compressor to see how it would perform in these applications.

Meller Flow Trans (MFT), a Bradford, West Yorkshire, UK-based distributor for Mouvex, chose Lomas Distribution to field test the MX12 screw compressor. The goal was to see if a compact, truck-mounted screw compressor could consistently and reliably provide enough air pressure to unload difficult dry bulk products. Founded in 1960, MFT focuses on and specialises in developing liquid-based and powder-based product-transfer solutions for the transport market, regardless of industry.

Kevin Mears, a veteran transport truck driver, got to experience the capabilities of a screw compressor on his vehicle first-hand. His first experience came from offloading ferrous sulfate, a granular product that requires lots of air. When using the MX12, his best time was moving 29 t of product in 22 min.

This was not the only product he tested the MX12 on either. When he was transporting fly ash, a byproduct of burned coal commonly found in cement, he was able to offload 22 t in 15 min.

These unloading times are possible because of the screw compressor’s 29 psi (2 bar) air pressure, allowing it to achieve flowrates of up to 1130 m3/hr (18 833 l/min.). Those performance features allowed Mears to, on average, unload a 28 t trailer in 35 - 45 min., a process that previously took him more than an hour to complete.


The demands for stricter emission requirements and lighter and more compact vehicles likely will not lose momentum in the near or distant future. Space on these vehicles is at a premium for a reason and essential equipment such as screw compressors should not be sacrificed for less effective technology.

The Mouvex MX12 is an example of a screw compressor that provides the footprint and performance needed to help operators with their bulk transport needs without the need to compromise on efficiency or functionality.

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