Metering pumps
ATEX compliant diaphragm pump with integrated protection system

The German pump manufacturer LEWA recently released a new metering pump program. The main new features of this series are the new drive units and the completely new developed diaphragm pump head with PTFE diaphragm and DPS (Diaphragm Protection System). The new design complies to the new ATEX directives.

The new M900 pump heads with PTFE diaphragm have an impressive suction ability for diaphragm pumps which is comparable to the ability of plunger pumps. this implies that the pumps are even suitable for pumping from vacuum. Basically the PTFE membrane pump heads are typical LEWA design and can handle pressures up to 400 bar. The safety and reliability are direct demands and the sandwich membrane construction is by this the standard execution (see figure 2).
Moreover, the hermetically sealed construction permits the use in problematic application fluids with properties like :
• bad lubrication properties (liquefied gasses, solvents)
• sterile liquids (injection preparation)
• valuable liquids (herb extracts, volatile oils)
• higher vapour pressure (liquefied gasses)
• reaction with atmosphere (Natrium, Aluminiumalkyl)
• radioactive liquids (Plutonium & Uranium solutions)
• explosive liquids (Hydrogen, Silane)
• toxic liquids (Chlore, Brome)
• abrasive liquids (suspensions with SiO2, Al2O3, catalysts, lapping pastes)
• corrosive liquids (HCl, HF, HNO3).

The metering pumps are characterized by its constant pressure performance curve. This means that the flow is almost independent from the working pressure and the flow is linear to stroke length respectively stroke frequency (see figure 1).

Diaphragm Protection System
The Diaphragm Protection System (DPS) consists of a newly developed and patent-pending design for the control of the diaphragm motion. It makes sure the diaphragm is always moving within an optimum operating range. Independent from external influences, e.g. problematic operation conditions, or improper operation it is ensured that the diaphragm movement does not exceed the specified limits. Premature damage of the diaphragm due to overstressing is prevented. The pump can be started with maximum or partial stroke without any problems even under extreme conditions, cfr. vacuum condition. The diaphragm protection system (DPS) also includes a diaphragm condition monitoring system in combination with a pre-shaped multi-layer PTFE sandwich diaphragm. The system serves as indication of damages of one diaphragm layer due to wear. Due to the second diaphragm layer of the sandwich diaphragm the pump is still hermetically tight and operation can be continued until repair is possible. Thus unscheduled loss of production is avoided.

Pump features
The advantages for such a construction design are listed as follows.
• High operation reliability
The membrane movement is controlled by the DPS and follows in spite of all process conditions the plunger movement.
• High process reliability
The membrane rupture detection system detects every wear damage. The pump remains hermetically tight due to the sandwich membrane construction and unit can continue running for a limited period of time without interruption.
• Simple and secure operation
under severe conditions; example vacuum in suction tank, failure conditions lead no longer to membrane damage.
• Models up to 400 bar
As the membrane systematically will position in its extreme rear end position.
• Operational
in hazardous, dangerous, high viscous abrasive or sensitive applications.
• Suction condition improvement
similar to plunger pumps - DPS avoids the pseudo-cavitation in the hydraulic part of the pump head.
• Long service intervals
because the preformed sandwich membrane is centrally driven and a rotation symmetrical deformation is obtained and less on the membrane itself.
• Easier membrane exchange
simply by screwing the membrane on its central driven element.
• Easy spare parts stock handling
due to higher spare parts utility and interchangeability between models.
• Suction pressure reliability up to 400 bar because the membrane is supported in its rear end position.
• High dosing accuracy and very high efficiency obtained by DPS avoiding the vapour building due to the pseudo-cavitation in hydraulic side and due to the typical performance curve shape (linear and constant pressure).

New ATEX compliant drive unit
The drive unit has also fazed changes in the design. The pump drive unit design is based on four models. For the multi-head units, the couplings between the drive units are continuously running in a common oil bath. This last point is typical design resulting from the new ATEX requirements, to which the new design is complying to.
The drive unit is the hart of the metering pump where the rotating motor movement is converted to the displacement movement. The drive unit permits the stroke frequency and stroke length adjustment permitting the flow control. The stroke frequency varies linear to frequency driven electrical motor variation (fix gear ratio of the drive unit). The stroke length can be manually, pneumatically or electrically adjusted during operation as well as during standstill. The stroke length adjustment is done by means of a spindle and positioning pin.
The drive unit is designed for a long life cycle, low maintenance time and cost. Here the common oil bath does not require radial sealing and eliminates wear parts resulting in lower maintenance.

Application range
The application range of this series covers a wide flow range from 1 l/h to 10 m³/h output per pump head. The maximum discharge pressure is 400 bar with PTFE diaphragms and 1200 bar with metal diaphragms. The temperature range is between –40°C up to +300°C with special designs. The pump can be selected for fluid applications with viscosity between 0.1 to 100,000 mPas.