Faced with the range of products that DKM has been asked to pump, we have developed an exclusive device, which protects a standard shock absorber from corrosion and abrasion. The technical advantages are as follows :

The pulses are transmitted hydraulically to the shock absorber.

The diaphragm rupture detection systems (sandwich or by resistivity variation) are still applicable.

The materials in contact with the fluid transported are identical to those used on the pump :
PTFE-coated nitrile diaphragms, or metal diaphragms, shock absorber chamber made from stainless steel, hastelloy, uranus, titanium or plastic (PVC - PP - PVDF), etc.

Mounting from the pump delivery can be horizontal or vertical.

Grid transparency and diaphragm flexibility ensure the same efficiency as when the shock absorber is mounted directly on the product.

The shock absorption chamber can be cooled or heated without problem. (To allow normal running at high temperatures, a finned cooler is fitted in between the bladder bottle and the separator).

Measurement devices can be fitted on the hydraulic part of the separator (pressure and/or temperature sensors), well out the danger from corrosion or abrasion phenomena.

SANDWICH DIAPHRAGM SYSTEM

We have been marketing a patented "sandwich diaphragm" system (French Patent No. 71.44363) for over 30 years.

Two diaphragms on the pumped-liquid side are held together, "sandwiching" a flexible detection capillary tube between them. One end of the tube is open to the outside and the other to the space between the two diaphragms. The outside end of the tube is connected to a visual indicator (sight glass), a pressure gage or a pressure switch .

Under normal conditions, no pressure exists between the "sandwich diaphragms" or in the detection system. However, should a tear occur, the pumped liquid enters the "sandwich" and the detection system at the discharge pressure.

The operator is alerted to the problem by the presence of liquid flowing from the detection system, a pressure indication on the pressure gage, or a signal from the pressure switch, depending on the option chosen.

The DKM system does not require maintaining a vacuum between the diaphragms, as is the case with other systems being marketed; therefore, it is not necessary to have a vacuum pump. In addition, the reliability of the system is reinforced, since there is no false rupture signal due to a poor vacuum.

This system is primarily adapted to pumping clear liquids. Also, the sensitivity of the pump is reduced due to the increased stiffness of the double-wall diaphragm.

RESISTIVITY DETECTOR:

DKM, which first filed in 1971 for a patent on a system for detecting the rupture of a sandwich type diaphragm, has since measured the limits of this system, particularly for thick or viscous liquids.

To supplement its product offering, DKM has now developed a system for detecting such rupture based on the variation of the resistivity of an intermediate safety liquid.

A probe is implanted in the intermediate plate, which enables, with its associated electronics, measuring the resistivity in real time.

A threshold alarm incorporated in the electronics monitors the variations of this parameter. The only role of the intermediate liquid is to hydraulically transmit the diaphragm movements. The resistivity threshold is adjusted on the latter.

Pollution of the intermediate liquid by diffusion through, perforation, or destruction of the process diaphragm leads to variation of its resistivity. This fact is immediately detected by an alarm module, whether the resistivity has decreased or increased.

Explosion-proof and CE in accordance with the INERIS certificate n° 98.D5070X
Test report : CE 14 152 - 3/1999
Classed : Eexd [ia] ia II CT 6

During shutdown, draining operations, even when accompanied by gas purge, can leave a small quantity of the dangerous chemicals in the pump and especially in the check valves, making the disassembly operation very dangerous.

The novel system patented by DKM, under the name "Reversible Check Valves", permits rotating the valves 180° by means of knobs attached to them, thereby allowing total draining through the inverted valves.

The innovation resides in the installation of the ball check/seat assembly in a ball valve to permit 180° rotation (see drawing to the right).

The reverse operation is performed to prepare the pump for operation.

This system requires no disassembly; the operator never comes into contact with the product and the manoeuvre is rapid and absolutely safe.

These reversible check valves, in the PVDF version, are especially adapted for bromine chemicals.

The materials available (plastics and metals) permit a large range of applications.

Different products necessitate different check valves.

Take as an example, the case of liquids containing suspended solids that have a tendency to settle out. Reverse pumping from top to bottom favours the product flow by avoiding the gradual build-up of particles at the bottom of the metering chamber and around the check valves. However, in the case of reverse pumping, the ball checks must be held in contact with their seats. The usual spring-loaded system adds an element that favours the fouling of the check valve.
DKM patented magnetic check valves avoid the use of springs, whose materials of construction are not always compatible with the products being pumped.

The ball checks are drawn against their seats located above them by a magnetised soft iron core, 100% clad in stainless steel (or other material compatible with the product being pumped). The magnetic field is generated by a stack of ferrite magnetic rings located around the outside of the check valve. These rings are positioned using a set of movable spacers that permit regulating the seating force of the balls.

Total removal of the spacers prevents the ball checks from moving off their seats. This facilitates pump filling and degassing without opening to the atmosphere.

The permanent magnetisation of the ferrite rings requires no external energy source. It permits continuous unlimited operation without any constraints.

The user must rely totally on the value displayed on the stroke-adjustment system, because the pump is, by definition, of the Volumetric type.

The factory-established calibration curve may not reflect exactly the flow rate values obtained in-situ , in view of the nature of the liquid being pumped and/or the intake and viscosity conditions.

In this case, the calibration pot enables calibrating the pump performances.

The calibration pot is installed on a tapoff of the intake line, downstream from a line valve, with an isolation valve at its foot and a vent valve at its summit.

The calibration pot can be made of graduated PVC or glass, shielded against shock, for small flow rates and low intake pressures, or

It can be made of steel, with an external level indicator, for large flow rates and high intake pressures.

PNEUMATIC SERVOCONTROL

In this case, the manual flow rate control device is replaced by a double-acting oleo-pneumatic actuating cylinder, whose travel is adjusted by a positioner, also of the pneumatic type. The undesirable mechanical pulsations are dampened by means of hydraulic dash pots, which are sort of oil reservoirs in communication with the cylinder chambers via narrow orifices. The compressed air delivered by the positioner is applied above the reservoir oil, to cause the desired movement of the cylinder, while attenuating the mechanical pulsations.
The positioner receives the 3 - 15 psig (0.2 - 1 bar) instrument signal as well as the 4 - 6 bar drive signal. This solution is effective for transmission over a short distance only; otherwise, the response time becomes unacceptably long.
It is possible to have backup local manual control, either mechanical (acting on the pump handwheel) or pneumatic, by substituting, via a three-way valve, a local control signal for the remote control signal.

SERVOCONTROL WITH ELECTROPNEUMATIC ASSISTANCE

This possibility resembles the preceding case, but the 3 - 15 psig signal is locally generated by an electropneumatic converter, which receives a 4 - 20 mA electronic control signal. The control signal can be transmitted over a long distance in this case, because the electronic signal circulates in a current loop. The compressed-air supply for the converter is constraining (in general, 20 psig) and must be of "control" quality: dry, clean, and oil-free. This can be ensured by means of a pressure-reducing filter.

ELECTRIC SERVOCONTROL

Multi-revolution rotating servomotors can be installed instead of the manual flow control device and make it possible to adjust the pump flow rate from 0 to 100 % of its range.
Schematically, a two-rotation-direction electric servomotor is controlled by a positioner, also electric, which receives the 4 - 20 mA analogical control signal.
The electric servomotor is equipped with the following standard accessories:
mechanical force limiters,
end-of-travel stops,
position-following controlled by the 4 - 20 mA analogical signal,
disengageable manual control.

The electric servocontrol requires a standard 400 V three-phase 50 or 60 Hz voltage supply. It exists in sealed IP 67 and ADF EExd versions.