2021-09-07
Background to Concrete Pumps
Over a period of more than half a century, concrete pumps have slowly taken over from other methods of transferring liquid concrete. A number of different designs of concrete pump were developed in the first half of the 20th century but it was Friedrich Wilhelm Schwing's company Schwing GmbH which invented the twin cylinder hydraulic concrete pump in 1957. The principle of this design was adopted by almost all other manufacturers and is still the worldwide standard design.
The pump works by one piston drawing liquid concrete into a cylinder from a hopper while the other one simultaneously pushes its concrete out into the discharge pipes. A valve which determines which cylinder is open to the concrete hopper and which one is open to the discharge pipes switches over each time the pistons reach the end point (see rock valve below and animation left - click to enlarge) and the process continues with the first cylinder now discharging and the second drawing fresh concrete from the hopper.
The Concrete Pump was particularly important in revolutionising the construction of large high rise buildings. Previously cranes had been employed to lift large buckets (or skips) full of concrete up to where it was needed. A crane could lift one bucket at a time, normally holding around 2 cubic yards of concrete.
There are many advantages in pumping concrete over this bucket and crane system. As well as being able to pump concrete much faster than buckets could lift it, it also means a constant supply of concrete to the top and the placing hoses can be positioned wherever they need to be so the liquid concrete can pour straight out of the hose where it's needed rather than having to distribute a two cubic yard mound of concrete over the desired area.
As demand grew for concrete to be pumped further and higher, the flat gate valve in use at the time could no longer cope with the pressures required and in 1982, Schwing patented the revolutionary "Rock Valve". This was able to work with far higher pressures, allowing the heights and distances for concrete pumping to be greatly increased. The high pressure in the Rock Valve system helps seal the valve rather than working against it.
The wide mouth of the Rock Valve also helps keep the system stable and is extremely low wearing due to the low friction design. The abrasive concrete is only scraping against one side of the valve at any one time, nearly halving the amount of wear compared to other designs.
Pumping the concrete is one aspect of the overall task. Another is controlling where the concrete is placed. Whilst this can be done by manually positioning the end hose, a remote-controlled articulated placing boom is often used to position the placing hose exactly where the concrete is needed. The robotic arm is designed to unfold is a small area and be able to reach every spot within the length of the boom. Even if there are difficult barriers and constraints in the area. The pipe runs the length of the boom and a placing hose on the end can be positioned to place the concrete precisely where it is needed, quickly and easily.
Other than capacity, the main difference between the various types of concrete pumps is determined by the additional equipment that comes as part of the pump. A concrete pump in its simplest form is best represented by a Stationary Concrete Pump. Additions to this, resulting in other types of concrete pump are:
A Mobile Concrete Pump, also known as a Truck Mounted Mobile incorporates both a concrete pump and a placing boom mounted onto a truck chassis. Mobiles come with booms ranging from less than 20 metres to ones which can reach heights of over 60 metres. The advantage of a mobile pump is that it can turn up at a job and be pumping concrete very quickly to anywhere within the range of the boom. This makes mobile boom pumps very popular on the widest range of construction projects, being able to pump at very high volumes quickly to wherever concrete is needed with minimum labour requirements.
A Static Concrete Pump, also referred to as a Stationary, Line Pump or Trailer Mounted Concrete Pump is mounted on a trailer and requires a separate pipeline to be attached reaching to wherever the concrete needs to be placed. The pipeline is a series of steel or rubber pipes, known also as concrete placing hoses, linked together and manually attached to the outlet of the pump. The other end of the pipe could either be attached to a Separate Placing Boom, allowing the concrete to be placed with precision quickly over a wide area or it might just finish with a rubber placing hose for manual placement. A Static Pump needs to be towed or separately transported to jobs.
The advantage of a static pump is that the pipeline can be long so that the actual pump can be very far away from where the concrete is being placed; maybe hundreds of metres below or even kilometres away. This makes static pumps essential for tunnelling work and high rise constructions. Static Concrete pumps come in a far greater range of capacity than those used on Mobile pumps. From smaller pumps ideal for residential and low rise work right up to the SP8800 which can reach pressures up to 243 bar and pump over 100m³ per hour. It is a middle of the range SP4000 which holds the World Record for pumping concrete to the highest vertical distance. (The job also included a horizontal component of over 1km.) A pumping distance has yet to be found which cannot be done by a Schwing pump.
A static pump can also be mounted onto a truck chassis but without a boom, resulting in a Schwing Truck Mounted Static Concrete Pump. These are perfect for the many quick jobs where a boom might not reach. It might be a slab for an extension at the back of a home or garden where running a pipeline through or round the building is the only option. A normal static pump would need to be towed or delivered on a Hiab truck but with the Truck Mounted Static Pump, the operator can drive it straight to site. Schwing Truck Mounted Static Pumps also come with storage for up to 100 meters of pipeline and other accessories so everything needed is in one place allowing the operator to pack up and head straight to the next job as soon as a work is completed.
Another aspect of concrete placement is the supply of concrete. Both Mobile and Static Pumps have a large hopper to receive concrete from a truck mixer. However Schwing Stetter offers a mobile product which also carries a supply of concrete with it. The Fahrmischer Beton Pumpen (truck mixer concrete pump) combines not only a pump and boom but also the concrete storage and transport in the form of a mixer truck, all in one package.
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