Wednesday, August 31, 2016

Kinetrol EL Positioner Option: Special Characteristic for Butterfly Valve Linear Flow Control

EL Positioner
EL Positioner

EL positioner option: Special characteristic to give butterfly valve control for linear valve flow vs. input signal.

Upon request Kinetrol can supply a positioner fitted with a circuit that will provide an output characteristic to suit a butterfly valve. By replacing the standard circuit (with 10 non-linear and one linear control response curves) by one containing a microprocessor programmed with 10 different non-linear curves and one linear, the valve can be controlled to give optimum flow control with a butterfly valve.

In general the pressure drop across a valve will change as the valve opens, and this changes the flow/valve position characteristic. The five solid line curves on the graph linearise the response for valve pressure drops which fall to a range of values as the valve is opened fully, see below.

The values below are the pressure drop with the valve full open expressed as a percentage of the pressure drop with the valve closed.
  • Curve -1 for 100% (this should be used to linearize a butterfly valve which is operating with a constant pressure drop)
  • Curve -2 for 30%
  • Curve -3 for 10%
  • Curve -4 for 3% 
  • Curve -5 for 1%
Click on graph for larger view.

A butterfly valve controlling the flow of a fluid with a 10% constant pressure drop, gives 50% of its fully open flow at an angle of opening of roughly 40 degrees. We would thus recommend the user set the control response to curve -3, here 12mA (half signal) would open the valve to 40 degrees to allow 50% flow rate. The user can select one of the eleven pre-programmed curves by going into SETUP mode.

Tuesday, August 30, 2016

Kinetrol + Plug Valve = Optimum Sludge Valve Performance

water treatment valves
Water treatment plant
Sewage sludge is the semi-solid material that is produced during sewage treatment of industrial or municipal wastewater. Sludge blowdown valves are used in water and wastewater treatment systems that separate solids prior to filtration. These valves are particularly susceptible to fouling and ultimately prone to failure.

Many valve manufacturers specify high-pressure/high-torque actuators to overcome the sludge. Many times they choose linear type valves and screw-type linear actuators because they provide the brute force needed to push through the sludge. An unwanted side-effect of using linear valves and actuators is that the same force used to push the disc through the sludge, also causes valve damage by pushing and grinding solids into the valve seats, disc and seals. Eventually, the valve becomes so damaged it no longer provides proper shut-off.

Kinetrol actuator
Kinetrol actuator
Pneumatic scotch yoke and rack and pinion actuators, with quarter-turn valves, can provide the torque required for opening and closing the valve, and the nature of some quarter-turn valve designs protect internal parts from damage. Plug valves are designed this way and when combined with double acting pneumatic actuators that operate on a controlled time frequency, are a very reliable design for this application. The cycle frequency depends on the amount of solids in the media, and cycle times of opening and closing every 20 minutes are common. This cycle rate however, is problematic for scotch yoke and rack and pinion actuators, causing them to fail prematurely. In some cases the actuators fail in only 3 - 4 months of use.

For sludge applications, Kinetrol rotary vane actuators mounted on quarter-turn plug valves are a great choice . The combination of the high cycle actuator design, with the design benefits of a plug valve, offer wastewater treatment operators a valve assembly that will provide years of trouble-free life.

Monday, August 22, 2016

Wednesday, August 10, 2016

Fit and Forget, Worry-free Pneumatic Valve Actuators

Here's a short, narrated introduction to the Kinetrol vane actuator and their use on industrial valves. Kinetrol's 60 years of applying "fit & forget, worry about something else" actuators has rightfully earned their reputation for being the most durable, long-lasting valve actuator on the market today - a statement backed by a 4 million cycle warranty and documented, real-world field installations where the actuator provided upwards of 30 million maintenance-free cycles.

For more information, visit