Concrete pump spare parts maintenance problem 

Concrete pumping maintenance and repair is an effective method to restore the technical performance, eliminate faults and hidden dangers, and extend the service life of the machinery. In addition to its own mechanical friction, concrete pump are also affected by various external forces and environmental erosion during operation, so various parts of concrete pump truck have a service life. 

However, there are still many technical problems in the concrete pump truck maintenance industry, which leads to low quality of mechanical maintenance and inability to fully restore mechanical performance, causing losses to consumers and even concrete pumping accidents. This article briefly analyzes the common technical problems encountered in concrete pump truck maintenance work, aiming to attract the attention of relevant personnel.

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Failure to correctly identify the cause of the concrete pump fault

Some maintenance personnel are not familiar with the structure and principles of construction concrete pump machinery. They do not carefully analyze the causes of failures and cannot accurately determine the location of the failure. They blindly dismantle the concrete pump machinery with the idea of "approximately or almost". As a result, not only the original failures could not be eliminated, but new problems arise due to poor maintenance skills and workmanship.

For example, one of the Putzmeister concrete pump had a problem with insufficient diesel engine power and mechanical inability to work. The maintenance personnel disassembled the PT fuel injection pump and injector but could not find the cause of the problem. They replaced the fuel injection pump for testing, but the problem still existed. Finally, it was found that the problem was caused by excessive impurities and water in the diesel used. However, the disassembly caused the performance of the PT fuel injection pump to drop significantly and the diesel engine power to be insufficient.

Therefore, when determining construction machinery failures, the "elimination method" and "comparison method" are generally used, in the order of simple to complex, first appearance and then interior, first assembly and then spare parts, and avoid "blindly dismantling and disassembling without asking right or wrong".

Blindly replacing parts for concrete pump maintenance

It is relatively difficult to judge and eliminate construction machinery failures. Some maintenance operator always use the method of replacing parts for testing. No matter whether the spare parts are large or small, as long as they think the parts may be the cause of the failure, they will replace them one by one for testing. As a result, not only the failure is not eliminated, but parts that should not be replaced are changed.

For example, a Schwing concrete pump truck was repaired due to a steering problem. The maintenance replaced the steering pump, overflow valve, steering cylinder and other parts but failed. Later, it was found that the cause of the failure was the oil hose aging, which caused insufficient hydraulic oil flow and pressure. There are also some faulty parts that can be completely restored to their technical performance through repair. For example, when a generator, starter, oil cooler fails, they can be repaired without complex repair processes. However, maintenance operator require users to replace new parts and blindly adopt the method of "repair by replacing parts", resulting in serious waste.

During maintenance, the cause and location of the fault should be carefully analyzed according to the fault phenomenon, and the technical performance of the repairable parts should be restored by repair methods, and the practice of blind replacement of parts should be avoided.

The problem of not checking the quality of new spare parts

Before replacing parts, some maintenance personnel do not check new spare parts and directly install them on concrete pump. This practice is unscientific. The quality of spare parts are varies  in the market, with some counterfeit and inferior parts being mixed in with genuine ones. And some parts have changed in performance due to long storage time. If they are not inspected, they often cause failures after assembly.

For example, a Sany concrete pump had a diesel engine with too low oil pressure. The analysis showed that the oil filter was blocked. The maintenance personnel replaced a new oil filter, but the oil pressure was still low after the test. Finally, the cause of the failure was not found, and the engine was used with low oil pressure, resulting in the burning of the diesel engine, the breaking of the crankshaft, and the bending of the connecting rod, resulting in a lot of loss.

After inspection, it was found that the replaced oil filter element was blocked with too much rust, because the filter was stored in the warehouse for a long time, resulting in internal rust. Therefore, before replacing new concrete pump parts, necessary inspections and tests must be carried out, including appearance and performance tests, to ensure that the new parts are fault-free and to prevent unnecessary troubles caused by them.

The phenomenon of spare parts misusing

When repairing concrete pump, the phenomenon of substituting or misusing parts is still common. Some spare parts can be used as emergency substitutes, but long-term use is harmful and affects the safety and technical performance of the concrete pump. Some maintenance people have little understanding of the structure and principles of the machinery. Many parts do not match the model, but they think that as long as they can be installed, they will be fine, without considering whether the technical performance of the machinery can be brought into play.

For example, if a single-layer concrete pump pipe is used instead of a twin wall concrete pipe, the pressure of the single-layer pipe will not meet the specified requirements, and there will be many risks of pipe explosion. The DN200 wear plate was mistakenly used as a DN230, resulting in coupling mismatch and serious damage to the pumping system.

Using defective products instead of qualified spare parts, using iron wires and nails instead of split pins, using steel bars and old bolts instead of cylindrical pins, etc., the concrete pump spare parts quality cannot be guaranteed and long-term use is absolutely not allowed. Therefore, when maintenance repairing concrete pump, genuine spare parts should be used as much as possible, and other model accessories should not be used as substitutes, let alone misuse.

Confusing use of bolts in concrete pump

When repairing concrete pump, it is quite common to misuse bolts. Because the performance and quality of the bolts do not meet the technical requirements, mechanical failures often occur after repair. Special bolts used in concrete pump, such as transmission shaft bolts, cylinder head bolts, connecting rod bolts, flywheel bolts, injector fixing bolts, etc., are made of special materials through special processing. They have high strength and strong shear resistance, ensuring reliable connection and fixing.

In some maintenance operations, when some maintenance personnel find that these bolts are damaged or missing, they cannot find standard bolts for a while, and some randomly take other bolts to replace them. These bolts have poor material or unqualified processing technology, which leaves hidden dangers of failure in the use of concrete pump. Some parts need to use "fine-pitch" "fine-thread self-tightening" bolts, copper bolts, and copper-plated bolts, but ordinary bolts are used instead, resulting in bolts loosening and difficulty in disassembly.

Some technical requirements stipulate that new bolts must be replaced after several disassembly and assembly. Because maintenance personnel do not understand these situations, repeated use of unqualified bolts can easily lead to mechanical failures or accidents. Therefore, when repairing concrete pump, if bolts are lost, they should be replaced with bolts that meet the requirements.

Problems with gap fit of spare parts

There are strict requirements for the gap between the concrete delivery cylinder piston and the cylinder tube, the "three gaps" of the piston ring, the piston top clearance, the plunger clearance of the oil engine, the brake shoe clearance, the master and slave gear meshing clearance, the bearing axial and radial clearance, the valve stem and valve guide clearance, etc. All types of engines have strict requirements and must be measured during maintenance. If concrete pump parts do not meet the clearance requirements, it must be adjusted or replaced.

For example, if the gap of the injection pump plunger is too small, when the temperature of the diesel engine rises, the plunger expands and conflicts with the oil delivery valve, and cannot reciprocate normally to supply fuel, and the engine stalls automatically. After the engine is shut down and cooled, there is a certain gap between the plunger and the oil delivery valve, and fuel can be supplied normally.

In some maintenance work, there are many cases where spare parts are assembled blindly without measuring the clearance, which leads to early wear or erosion of bearings, burning of diesel engine oil, difficulty in starting or explosion, broken piston rings, collision of parts, oil leakage, air leakage and other faults. Sometimes, even the improper gap of parts may cause serious damage to the concrete pump.

The problem of matching replacement parts not being a set

There are many matching parts on the concrete pump, such as the plunger pair, oil outlet valve pair, and injector needle valve pair of the diesel engine fuel system; the valve block and valve stem in the hydraulic control valve; the wear plate and cutting ring of the pumping system, etc. These mating parts are specially processed and ground in pairs during manufacturing. They are very precise in matching and are always used in pairs during their service life. Some mating components, such as pistons and cylinder sleeves, etc., have a relatively good match after a period of working. During maintenance, they should also be assembled in pairs.

If these parts are used together as a set, they must be replaced as a set if they are damaged. Otherwise, due to the large difference in quality, age, length and size of the parts, the diesel engine will run unsteadily, the hydraulic system will leak oil, the load concentration will be serious, and the replaced parts will be easily damaged at an early stage.

In maintenance work, some people do not replace the above-mentioned parts as a complete set in order to reduce expenses or some people do not understand the technical requirements, which reduces the maintenance quality of concrete pump, shortens the life of replacement parts, and increases the possibility of failures.

The problem of reverse installation of spare parts

When repairing concrete pump, some parts have strict directional requirements for assembly. Only correct installation can ensure the normal operation of the parts. Some parts have unclear external features and can be installed in both directions. However, they are often installed in reverse in actual work, resulting in early damage to parts, malfunction of machinery, damage to concrete pump

Such as engine cylinder, piston, piston ring, thrust washer, thrust bearing, oil deflector, fuel injection pump plunger, drive shaft universal joint, etc., these parts are most likely to be installed upside down if the structure and installation precautions are not understood, resulting in abnormal operation after assembly and causing concrete pump failure.

For example, the working oil pump of the Zoomlion concrete pump is equipped with two skeleton oil seals. The correct installation direction of the oil seal is: the inner oil seal lip faces inward, and the outer oil seal lip faces outward. This can prevent the working pump from pumping the oil in the hydraulic oil tank into the gearbox through the speed change pump, and also prevent the speed change pump from pumping the oil in the gearbox into the hydraulic oil tank through the working pump. Therefore, when assembling parts, maintenance personnel must understand the structure and installation direction requirements of the parts and must not install them blindly as they please.

Incorrect selection of maintenance method for spare parts

When repairing concrete pump, some maintenance operator do not adopt the correct maintenance methods, believing that emergency measures are omnipotent, and replace "maintenance" with "emergency", and there are still many phenomena of "treating the symptoms but not the root cause".

For example, when the connecting thread of the hydraulic cylinder earring and the piston rod is damaged, the direct welding method is used, which makes it impossible to replace the cylinder oil seal after it is damaged, resulting in serious oil leakage. When the working device is found to be slow in movement or difficult to turn, the maintenance personnel do not check the cause of the fault and blindly increase the working pressure of the system, resulting in excessive system pressure, which is easy to damage the oil seal, pipeline, hydraulic components, etc. In order to make the diesel engine "more powerful", the fuel supply of the injection pump is increased and the injection pressure of the injector is increased artificially.

These irregular maintenance methods can only be used as an emergency measure, but cannot be used for a long time. It is necessary to find out the cause of the fault fundamentally and adopt regular maintenance methods to eliminate the fault.

Improper use of gaskets and washer

There are many types of gaskets and washer used between the mating surfaces of concrete pump parts. Commonly used ones include rubber gasket, cardboard washer, cork washer, felt washer, copper washer, aluminum washer, copper-skinned asbestos disk, insulating washer, spring ring, etc.  Some are used to prevent oil, water and air leakage between the mating surfaces of parts, and some are used to tighten and prevent loosening. There are different regulations and requirements for the timing and occasions of using each type of gasket washer. When repairing concrete pump, the phenomenon of improper or even abused use of gaskets is still quite serious.

If spring gaskets, locking gaskets, and sealing gaskets are not installed, the joints are not tight, which is prone to loosening or oil leakage. If the engine cylinder gasket is too thick, the compression ratio will be reduced and the engine will be difficult to start. Copper gaskets are used between the injector and the cylinder head mating surface. If asbestos gaskets are used instead, the injector will be easily burned due to poor heat dissipation. If the gasket between the diesel engine fuel pump and the injection pump is too thick, the fuel delivery volume and fuel delivery pressure will be insufficient, and the diesel engine power will decrease.

Here we would like to remind all maintenance operator that when repairing concrete pump, they must remember that "gaskets are small but very useful".

The poor quality of "small spare parts"

During maintenance work, some maintenance people often only pay attention to the maintenance of components such as injection pumps, oil pumps, pistons, cylinder liners, hydraulic pumps, control valves, brakes, steering systems, etc., but ignore the maintenance of "small parts" such as gasket, filters, overflow valves, and various instruments. They think that these "small parts" do not affect the work of the machine, and it does not matter even if they are damaged. It is the lack of maintenance of these "small parts" that causes early wear of the concrete pump and shortens its service life.

For example, the air filter element of a Sermac concrete pump was damaged, and the operator did not replace it in time. The machine was not used for a long time, and the power of the diesel engine decreased. Inspection found that the piston, cylinder, piston ring, valve were severely worn.

Therefore, these "small parts" are essential for the normal operation and maintenance of construction machinery, and are crucial to extending the service life of the machinery. Such as the oil filter, air filter, hydraulic oil filter, water temperature gauge, oil temperature gauge, oil pressure gauge, sensor plug, sensor, alarm, preheating plug, oil filter, water tank cap, oil tank cap, oil filling port cap, grease nipple, gas cylinder drain switch, battery box, injector return oil joint, cotter pin, fan air guide cover, transmission shaft bolt lock plate used in concrete pump.

Incomplete cleaning of parts

When repairing concrete pump, correctly removing oil and impurities from the surface of parts is of great significance to improving the quality of repair and extending the service life of the concrete pump machinery. Due to the lack of attention to the cleaning of parts, early wear and corrosive damage of parts often occur in some maintenance.

If the cylinder liner steps, carbon deposits in the piston ring grooves, debris in the bolt holes, and sand in the hydraulic components are not thoroughly removed, the bolt torque will be insufficient, the piston ring will break easily, the hydraulic cylinder gasket will be burned, and the hydraulic components will wear out prematurely.

When cleaning spare parts, maintenance personnel must first select the correct cleaning agent. Different cleaning agents should be selected according to the parts requirements for cleanliness. Do not use alkaline cleaning agents to clean aluminum alloy parts, and do not use strong acid cleaning agents to clean copper parts to minimize corrosion of the parts.

When repairing concrete pump machinery, if you do not pay attention to clearing the oil or impurities accumulated in the diesel filter, oil filter, hydraulic oil filter, diesel engine water jacket, radiator surface, lubricating oil channel, it will reduce the operating time of the concrete pump machinery.