Lapping of a control valve

Most of the control valves give sealing by the metal to metal contacts. Due to cavitation, flashing, erosion, or unidentified causes, the gap will be produced between the plug and seating.

seat for lapping

Such a gap or scratches will causes leaking and free movement of a control valve or ON-OFF valves. Lapping is the only way to eliminate such things. Lapping is the process of controlled grinding using lapping paste. Lapping paste is a mixture made of different grades of Carborundum which is generally harder than the silica sand. There are different grades depending on how hard the lapping to be done. The grades are coarse, medium, hard, fine and super fine.

The process of lapping is done by applying a little paste on the seating portion of the plug.

Put the plug and bonnet back.

Connect the handle of lapping set to the stem

Apply slight force and make half rotation in both clockwise and anti clock wise directions

After making 5 to 10 rotations take the plug outside and clean it

Repeat the process until the stem and seat becomes fine without scratches by applying proper grade of lapping paste.

Now a day the lapping is done by using sophisticated lapping machines as shown below

different lapping tech

Parameter setting of  E+H LT

Parameter setting of E&H FMP51 GWR LT

Siemens LT parameter setting

Parameter setting of Siemens Probe LU Ultra sonic Level Transmitter

Parameter setting of KTek LT

Parameter Setting of KTEK MT 5100 GWR LT

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Analysis of motor/pump vibration

HART Communication

HART Communication

Instrumentation tube fittings

Radar LT non contact type

Rosemount GWR parameter setting

Offset calculation GWR

Temperature transmitter types

Flow transmitter types

Level transmitter types

Pressure  transmitter types

Piping and Instrument diagram

Smoke detector working


Conductivity transmitter working

Gas detector working

Flame detector working

Units and conversion

Specific gravity

Instrumentation Interview questions

Temperature transmitter calibration

Pressure transmitter calibration

Magnectostrictive LT calibration

Hazardous area classification

Excel short keys

Digital electronics

Thermocouple mV conversion chart

Foundation field bus

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Root cause Analysis

Shore Key Line up

pH Analyser

Mathematic Formula


Oil in Water Analyser

BSW Analyser

Capacitive Level Transmitter

LRV and URV Level Transmitter

Instrument Loop Diagram

Laser Level Transmitter

Turbine Flow Transmitter

Zero Suppression and Elevation

Bently Nevada 3500 VMS

Control Valve Servicing

Safety Integrity Level

Instrumentation Working Principle

Instrumentation Gland Sizes

LRV and URV of DP level transmitter

Instrumentation working principle continued

Level measurement using Pressure gauge

Tips and tricks in field Instrumentation

Data Communication Protocol

Pressure Unit Conversion

Calibration of  GWR level transmitter

Control Valves

ERS Level transmitter Parameters

Calibration of wet leg tube Level transmitter

Calibration of capillary type Level transmitter

mV conversion chart

Gulf JOB


Reynolds Number

Calibration of displacer type LT

My profile

Chemical hazard pictogram

RTD conversion chart

Ingress Protection


To know more about Instrumentation and Control,




Basic Instrumentation and Calibration


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