PILOTS AND ACCESSORIES

PILOT BLEED RATE

www.kimray.comBulletin No. Y09201

Issued 7/11Current Revision:Add 8" & 10" to chart

We are occasionally asked to furnish information concerning the “bleed rate” of our controllers. Our pilots or controllers do not have a continuous bleed rate. There are basically three kinds of pneumatic controllers: continuous bleed, actuating or intermittent bleed, and self-contained. The continuous bleed type uses a stream of gas which is constantly flowing through a tiny nozzle to atmosphere. Near the set point a small flapper moves close to the nozzle causing back pressure which works internally to actuate the device being controlled. The intermittent bleed controller utilizes a tiny three-way valve which is closed at both ports when conditions are as required, open to the actuator when an output is required, or open to atmosphere when pressure at the actuator needs to be relieved. With intermittent bleed, the question of the rate at which gas is emitted to the atmosphere has no easy answer. Other questions must be answered first. Is the controller throttling, or is it an on / off de-vice? If it is throttling, then only very small amounts of gas will be vented as the controller makes minute adjustments on the actuator’s position. This will vary with the size of the actuator and the stability of the system. If the controller is operating in on / off service then the following questions are vital: How often does the controller switch? What is the capacity of the actua-tor? What is the volume of the tubing which runs from the controller to the actuator? What is the pressure of the actuating gas? In either case with an intermittent bleed pilot, the only information that can come from the manufacturer is the capacity of the actuators. That information is the subject of the table in the next column.

Kimray Intermittent Bleed Pilot The key to accurate, consistent control in every Kimray pilot is the Pilot Plug. It functions as the plug in a tiny three-way valve, either communicating sup-ply pressure to the actuator of a controlled device, or venting pressure from that actuator. The balls at either end of the plug are stainless steel. The seats which these balls act to close are also stainless steel.

Metal to metal seat The use of steel for both the seats and plugs produces a metal to metal seat. A metal to metal seat is used in order to eliminate hysteresis, which would be seen as a lag or “dead-band” in the controlled pro-cess. Due to the nature of the design of the pilot, the plug is only lightly pressed into either seat. This also is done to eliminate hysteresis.

Seepage The very elements of design which allow the pilot to operate without any detectable dead-band or lag in control, do not allow for the necessary elements for tight shut-off. For this reason a small amount of gas will normally seep from the vent of the pilot. This does not affect the action of the pilot. Kimray describes the pilots as “intermittent bleed pilots”. This is to contrast them with the “continuous bleed pilots” which are found in some control devices of other manufacture. Unlike the continuous stream of gas characteristic in these devices the small amount which seeps from a Kimray pilot is considered normal.

Valve Actuator Gas CapacityFollowing is a simple table listing the capacity of the actuator of various Kimray valves and regulators. Of course the limitations of this information need to be recognized. There is additional information which must be supplied : • The frequency of actuation of the valves • The extent of actuation travel that regulators may require. (Often almost no movement is required) • The pressure of the actuating gas supplied • The volume of the tubing involved

DEVICE SIZE ACTUATOR CAPACITY CU. IN.

Regulator Catalog

Section A

1" 1.12" 93" 314" 736" 244

Regulator Catalog Section

E1

1" 302" 1103" 2254" 2436" 6508" 650

10" 650

Regulator Catalog Section

E2

1" 1.12" 93" 314" 736" 244

Regulator Catalog Section

E3

PO PC2" 6 83" 22 314" 27 366" 40 54