Part 1: Fuel consumption of piston pumps and Diesel vacuum aggregates

In daily sales business it often happens that the customer has already been advised by a colleague from another manufacturer. Particularly in the range of dewatering certain keywords like “1 litre Diesel per hour” and “90 m³/h max. discharge flow“ seem to eliminate all questions with the customers.

In such cases it is a pleasure for the HÜDIG sales persons to share their know-how about dewatering technique with the customer.

First it is important to know the active principles of vacuum-supported dewatering and of piston pump technique.

There are suppliers in the market stating water volume flow rates of 90 m³/h. Apart from the fact that these are not reached in practice anyway, the flow rate with groundwater lowering applications is actually only 30m³/h due to entrapped air deposits.

This cross section shows clearly the route of the pumping medium within a piston pump as well as the valve system which ensures that the pressure in the system is kept. It can be obtained from the cross section that due to construction the air cannot be separated from the water.

Apart from that, double-acting piston pump does not mean that this is equipped with two pistons, but that the medium is pumped on the backside and on the front side of the piston with pressure and suction effects, secured by the complex valve system.

By comparison, a vacuum system already separates the air content from the pumping medium due its design.

The well constructer appointed by a builder will be paid according to the system of the dry excavation pit or depending on pumped cubic metres. The air content in the pumping medium should not play any role in this case. In order to determine the actual discharge flow it is absolutely necessary to install a sand trap and a water meter in case of using a piston pump.

The installation efforts are quite considerable as shown on the following photographs!

Complex installation pump, sand trap and even incorrectly installed water meters. The water meter counts air! On the one hand side a higher water flow is presented to the customer and on the other hand side the client has to pay higher disposal costs!

The actual discharge flow is the reason why it is often necessary to install several piston pumps on construction sites in order to achieve the dewatering target.

The cross section of a vacuum aggregate’s operating principle shows how the water is separated from the air before leaving the system. It is therefore secured that nearly 100% water content leave the pressure stud. The vacuum support ensures additionally that the necessary air performance is produced in the system.

If we take a look at the argument of fuel consumption of approx. 1 litre per hour for the piston pump system - knowing how much a piston pump actually pumps – the real fuel consumption of a piston pump does not seem to be quite economical.

At corresponding motor load the fuel consumption raises to comparable 2,5 to 2,7 litres per hour, even with a motor speed of 1500 rpm. Thus, 90 m³/h (pure water performance) for a dewatering will not be reached!

The HÜDIG Diesel vacuum aggregate of type HC 522 can be operated between 1500 and 2300 rpm. At highest speed the one-cylinder Hatz Diesel motor needs max. 3 litres / hour and at the same time pumps V max. 110 m³/h and grants a vacuum support of further 58 m³/h air performance, in total 168 m³/h max. discharge flow (mixture).

In comparison with piston pump technique the installation is rather simple and easy. A piston pump has a weight of nearly 1,9 t, while the Diesel vacuum aggregate HC 522/07 with fully filled tank has a weight of 1,2 t and does not need any additional sand trap to measure the actual pumped water amount.

Only the pump counts!

In Part II we will report about the secret of noise measuring and noise level indications.