Flow can be adjusted from 0 to 100 % by varying the piston stroke variation manually and locally, a standard feature on DKM pumps.

Servo controls are standard accessories that enable the flow to be adjusted remotely or controlled by a regulator.

DKM – Clextral offers three types of servomotor for its pumps:

Pneumatic servo control

The manual flow adjustment system is replaced by a dual-action oleopneumatic cylinder, adjusted in mid-stroke by a positioner, which is also pneumatic. Unwanted mechanical pulses are damped by a hydraulic dashpot, a sort of oil reservoir connected by narrow openings to the cylinder chambers. The air from the positioner is applied to the top of the oil reservoir to achieve the desired movement, attenuating the mechanical pulses.

The positioner receives the instrument signal, 3 – 15 psig (or 0.2 – 1 bar), and the power feed at 4 to 6 bar. This is an effective solution for short-distance transmission, possibly with the risk of an unacceptably long response time.

A “local” manual restart is possible, either mechanical (by the pump handwheel), or pneumatic, replacing, via a three-way valve, the control room signal by a locally sent signal.

Servo Control with Electropneumatic Assistance

As above, but the 3 – 15 psig (or 0.2 – 1 bar) signal is generated locally by an electropneumatic converter which receives a 4 – 20 mA electronic signal. This enables long-distance transmission, with the electronic signal circulating in a current loop.

The converter’s air supply is restrictive (20 psig usually), of “regulation” quality, dry, clean and oil-free. This can be achieved by a pressure-reducing filter.

Electrical Servo Control

There are multiturn rotary servomotors which can be fitted in place of the manual flow adjustment system and which cover the entire 0 to 100 % range.

Basically, a two-way electric servomotor is controlled by a positioner, also electric, which receives the 4-20 mA analogue control signal.

The electric servomotor is fitted as standard with the following accessories:

  • Mechanical stress limiters
  • End of travel position recopy by 4-20 mA signal
  • Position recopy by 4-20 mA signal
  • Disengageable manual control

The supply voltages are standard 400V – tri 50 or 60 Hz. They are available in IP 67 and ATEX sealed versions.

If you are interested in the servomotors, please contact our Sales Department