Axelson ESP Pilot Pressure Sensor – Safety Shutdown
The Axelson ESP Pressure Sensor is a highly accurate and reliable device designed to detect an abnormal operating condition in a safety system and transmit a signal to perform a specific shutdown function.
The Axelson Pressure Sensor or pilot is a 3-way block and bleed valve that is controlled by a piston and spring.
The sensor is a highly accurate and reliable device that has a sensing pressure range of .25 to 20,000 psig.
It is used to sense predetermined pressure and, when that pressure is reached, shift the 3-way valve.
The actuation point is easy to adjust by turning the adjustment cap. This changes the spring force. Turning the cap clockwise will increase the pressure setting. Turning the cap counter clockwise will decrease the pressure setting.
The sensor may be used to detect high pressure or a low-pressure conditions by connecting the input instrument pressure to the appropriate port. When connected to either port the remaining port becomes the exhaust port.
Axelson ESP pressure sensor – Pilot Pressure Sensor – sensor and relay combination – Safety Shutdown
Two Pilots can be connected in a series and used for both high and low sensing. The combination high and low pilot is called the ESPHL.
ESP Programmed as a LOW PSL Pilot
Instrument pressure is connected to the port stenciled “LO.” The port stenciled “OUT” is connected to downstream safety components. The port stenciled “HI” acts as an exhaust port. The spring applies a downward force against the stem holding the pilot in a block and bleed position. Line pressure at Port D acts against the lower piston to create an upward force. Once the upward force exceeds the downward force of the spring, the stem will move upward opening the LO Port to the OUT Port to actuate downstream safety components. The pilot will remain in an open position until pressure at Port D drops below the low pressure setting of the pilot.
ESP Programmed as a HIGH PSL Pilot
Instrument pressure is connected to the port stenciled HI and the port stenciled OUT to downstream safety components with the LO Port acting as an exhaust. With flowline pressure below the high pressure set point of the pilot, the HI Port is open to the OUT Port, allowing instrument pressure to pass to downstream safety components. The spring will hold the pilot in an open position until flowline pressure activating the pilot piston exceeds the downward force of the spring. Once line pressure at Port D increases above the set point, the stem is forced upward, blocking instrument pressure at the HI Port and back bleeding instrument pressure through the OUT Port to the LO Port, causing the safety system to react. The pilot will remain in a block and bleed position until flowline pressure drops below high pressure set point.
The schematic illustrates a typical high-low safety shut-in system that uses an Axelson DG-3 diaphragm-operated gate valve, a pair of high-low sensors, and a PRV relay.
Sensing pressure range from .5 to 20,000 psi
Instrument pressure range up to 200 psi
Block-and-bleed 3-way valve
Designed for 3% repeatability of set point, or 5 psi, whichever is greater.
Minimum spread (dead band) between trip and reset pressure
Spring maybe be replaced with instrument and sensing pressures present
Vent in lower housing provides warning if body is accidentally loosened from lower housing with sensing pressure present
Available to conform to NACE Standard MR-01-75
Corrosion resistant 316 stainless steel used throughout with Inconel spring optional.
Sensing pressure connections:
9/16″ HP on high-pressure sensors (20,000 psi)
¼” NPT on low pressure sensors (diaphragm type)
½” NPT on all other sensors
Metal-to-Metal seal between stem and body is designed to prevent flow line pressure or fluids from entering instrument pressure system if O-ring seal fails when sensor is in Fail-Safe Position
Vent acts as a warning allowing sensing pressure to bleed out prior to disengaging body from piston housing
High Flow ESP
The ESP Sensor is also available with a high flow rate. The High Flow Rate Body provides increased flow capacity and increased pressure capacity through the instrument ports. This allows the sensor to be used as a block and bleed valve with faster reaction times for the system. It may also be used as a 2-way valve on a bleed only system.
Instrument Pressure – 600 psi Maximum
Instrument Pressure Range
Standard Body …………. 200 psi max.
High Flow Rate Body …… 600 psi max.
NOTE: When using a urethane o-ring on the stem – 1,480 psi maximum instrument pressure.
Repeatability to Set Point
within 3% of set point
Cv Factor (Flow Capacity)
Standard body …….. 0.028
High Flow Rate Body ….. 0.058
Dead Band (Spread) ……………………. Percent of Range
1 1/8, 1/2, 1/4 in. Pistons ……………. 5%
Diaphragm Types …………………………. 3%
3/16 in Piston ……………………………… 10%
AXELSON ESP SPRING COLOR CHART:
ULTRA LIGHT – WHITE SPRING
LIGHT – ORANGE SPRING
HEAVY – BLUE SPRING
RECOMMENDED PREVENTATIVE MAINTENANCE FOR THE ESP SENSOR:
(1) Cycle Test once a month or more often if service dictates.
(2) Disassemble, inspect all parts, and replace O-rings annually or more often if service dictates.
TO ORDER ORING KITS –
ESPVITONKIT – Viton O-ring Kit
ESPBUNAKIT – Buna O-ring Kit
Urethane O-ring needs to be specified and can be added to the kit.
(3) To change spring: with flow line pressure at port D, loosed locknut and remove the cap. Replace spring and reassembly. (See spring part numbers below.)
Spring Part No: (2nd Digit)
41047 – Light-Steel Spring (Orange)
41048 – Heavy-Steel Spring (Blue)
41049 – Light-Inconel Spring (Yellow)
41050 – Heavy- Inconel Spring (Green)
46301 – Ultra-Light-Steel Spring (White)
AXELSON ESP SENSOR IN THE FIELD
The ESPHL Sensor Unit provides a means of mounting two sensors in series to perform a “High – Low” PSHL function. It also provides a single mounting point. A variety of ESP sensors may be mounted on the control block. Sensors adaptable are the diaphragm, high flow, or standard. The mounting base has a maximum working pressure of 10,000 psi and a test pressure of 15,000 psi. It is available in carbon steel
and stainless steel and has ll2-in. NPT female mounting connections.