Fisher™ 4660 High-Low Pressure Pilot

Base/Case: Nitrile

Operating Conditions(1)

Condition

Normal Operating Limits

Ambient

Temperature-59 to 71C (-75 to 160F)

Nominal

Reference

21C (70 F)

Operating Influences on Switch Point Sensitivity

Supply Pressure: ≤0.05% of Bourdon tube rating for a

10% change in supply pressure

Ambient Temperature: ≤2% of Bourdon tube rating

throughout normal operating limits with nominal

reference

Time: ≤1% of Bourdon tube rating over 30 days at

ambient temperature nominal reference

Process Pressure: Range shift or set point drift can

occur if process pressure exceeds the Bourdon tube

rating

Pressure Connections

1/4 NPT internal

Mounting

Panel,

rack,

pipestand, or actuator

Specifications (continued)

Hazardous Area Classification

Complies with the requirements of ATEX Group II

Category 2 Gas and Dust

Ex h IIC Tx Gb

Ex h IIIC Tx Db

Maximum surface temperature (Tx) depends on

operating conditions

Gas: T6

Dust: T71

Meets Customs Union technical regulation TP TC

012/2011 for Groups II/III Category 2 equipment

II Gb c T*X X

III Db c T*X X

Safety Instrumented System Classification

SIL3 capable  certified by exida Consulting LLC

Approximate Weight

2.3 kg (5 pounds)

Options

Visual output indication stainless steel panel

mounting flange, set point indication, and

tamper-resistant front cover

Principle of Operation

Refer to figure 3.

Process pressure is connected to the Bourdon tube

sensing element. While the process pressure remains

in the adjusted set ranges (between the low set point

and the high set point), the flapper does not contact

either set point pivot. This keeps the nozzle capped

and maintains full output pressure.

As the process pressure decreases below the low set

point value, the radius of arc of the Bourdon tube

contracts. This causes the flapper to contact the low

set point pivot and uncap the nozzle, which blocks

supply pressure and vents (bleeds) output pressure. As

the process pressure increases above the high set

PROCESS PRESSURE

LOW SETPOINT ADJUSTMENT

HIGH SETPOINT

ADJUSTMENT

SPRING

BLOCK AND BLEED

RELAY ASSEMBLY

SUPPLY PRESSURE

OUTPUT PRESSURE

point value, the radius of arc of the Bourdon tube

extends. This causes the flapper to contact the high set

point pivot, also uncapping the nozzle and providing

block-and-bleed action. When the process pressure

returns to the set range, the nozzle is again capped,

switching the relay back to maintain full output

pressure.

Performance

The performance characteristics discussed in the

Performance in Percentage of Bourdon Tube Rating

specification on page  3 and shown in figure 4

illustrate several important functional parameters.

SL represents the low set point and SH represents the

high set point. The set range capability is 3 to 97

percent of the Bourdon tube rating. However, with a

single high-low unit or a high-only/low-only pair, there

is a limit on how close to each other the set points can

be adjusted. This limit is defined as set point ΔPMIN and

is shown as SL′ and SH′.

Trip-to-reset is the combined effect of pilot deadband

and hysteresis. After the pilot has tripped, it

automatically resets when the process pressure

returns to the set range. However, full output pressure

is not instantaneous. The difference between the set

point and reset to full output pressure is the

trip-to-reset zone. This parameter is also a function of

the Bourdon tube rating as shown in figure 4 and

discussed in the Performance in Percentage of

Bourdon Tube Rating specification on page  3.

Repeatability is the switch point deviation around the

set point as a percentage of the Bourdon tube rating.

Applications

Figure 5 shows some of the many ways in which the

4660 high-low pressure pilot may be connected to

accommodate requirements for single and dual

outputs as well as single and dual process pressure

lines. Examples A and D in figure 5 show how a pair of

high-only and low-only pilots are connected to obtain

closer set points as specified by the set point ΔPMIN

values in tables 1 and 2. Example B or C shows

connections for a two-segment flow line configuration

that adheres to API Specification RP14C. Example E

shows a typical connection to an electrical pressure

switch

Installation

Normal installation is with the pilot mounted vertically

and the connections for process pressure, supply

pressure, and output pressure facing down. The supply

medium should be regulated dry air or natural gas with

solid particles removed.

Figures 6 and 7 illustrate the mounting dimensions

and the location of the pressure connections.

Ordering Information

When ordering, specify:

Application

Bourdon tube rating and material

Composition, pressure, and temperature of the

process fluid

Ambient temperature range

Description of application

Construction

Refer to the Specifications table. Review the

information under each specification and in the

referenced tables; specify the desired selection

whenever there is a choice to be made