Hydrodemolition Equipment
Andreas W. Momber, in Hydrodemolition of Concrete Surfaces and Reinforced Concrete, 2005
3.2.1 Structure of high-pressure plunger pumps
High-pressure pumps generate the operating pressure and supply water to the spraying device. Generally, they can be divided into positive displacement pumps and hydraulic intensifiers. Positive displacement pumps are standard for hydrodemolition applications. In Germany, as an example, almost 90% of all on-site devices are driven by positive displacement pumps. The most common form is a triplex (three plunger) pump as shown in Fig. 3.3. Major parts of a positive displacement pump are:
Figure 3.3. Structure of a high-pressure plunger triplex pump
(photograph: WOMA Apparatebau GmbH, Duisburg)- •
crank-shaft;
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pump head with low-pressure inlet valves and high-pressure outlet valves;
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high-pressure plunger conversion set;
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pressure regulator valves;
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switch valves;
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safety devices.
Life times of pump components depend on many parameters, namely water quality (see Table 3.1), maintenance regime, and operating pressure (see Table 3.3). Most critical to wear and life time is the solid amount in water; this is illustrated in Fig. 3.4. If solid content increases (e.g. due to an insufficient water filter system) cost for replacement parts (valve seats, seals, plungers) increases. Temperature is another critical parameter for pump operation. An increase in temperature increases the probability of mineral precipitation as well as of cavitation. The first aspect is illustrated in Fig. 3.5; a pump part eroded due to cavitation is shown in Fig. 3.6. Both processes are highly erosive to pump components, and temperature control devices, coupled to shut-off mechanisms, should be part of any pump unit.
Table 3.3. Typical life time values for plunger pump components (Xue et al., 1996)
| Pressure in MPa | < 30 | 20 ∼ 31.5 | 31.5–50 | 50–70 | 70–100 |
|---|---|---|---|---|---|
| Component | Life time in hours | ||||
| Plunger | 2500 | 2000 | 1500 | 1000 | 800 |
| Seal | 1500 | 1000 | 750 | 600 | 520 |
| Valve | 3000 | 2500 | 2000 | 1500 | 1000 |
Figure 3.4. Solid content in water and maintenance cost for plunger pumps
(source: Reliance Hydrotec Ltd., UK)Figure 3.5. Relationship between water temperature and mineral precipitation
(Zentrale für Unterrichtsmedien, Tübingen)Figure 3.6. Damage to a bearing due to cavitation erosion
(photograph: Neale Cons. Engr., Ltd., Dogmersfield)The pump head hosts the water inlet and water outlet valve arrangements. It consists regularly of corrosive-resistant forged steel, partly also of coated spheriodal graphite cast iron. Typical plunger diameters for on-site high-pressure plunger pumps utilised for hydrodemolition applications are between 25 mm and 40 mm. The plungers are made from coated steel alloys, hard metals or ceramics (the latter material is limited to rather low operating pressures).
Safety and control devices include safety devices and pressure-measuring devices. Safety devices prevent the permissible pressure from being exceeded by more than 2.0 MPa, or 15%. These devices include pressure relief valves or burst disks, respectively. Automatic pressure regulating valves limit the pressure at which the pump operates by releasing a present proportion of the generated volumetric flow rate back to the pump suction chamber or to waste. It should be used to regulate the water pressure from the pump and is individually set for each operator. Pressure-measuring devices directly measure and display the actual operating pressure.