High-Side and Low-Side Block Valves
Study note: the two block valves separate the process from a DP transmitter. High side is the higher-pressure connection. Low side is the lower-pressure connection.
Learning objectives
- Explain High-Side and Low-Side Block Valves in technician-friendly language.
- Identify where identifying the high-side and low-side block valves from the tap locations before either valve is moved appears in live plant work.
- Connect the topic to pressure measurement, calibration, or loop checking.
- Avoid the main field mistake: closing one block valve while the equalizing valve is shut and the other side is still at process pressure.
High-Side and Low-Side Block Valves is part of the Pressure Measurement master module. Study note: the two block valves separate the process from a DP transmitter. High side is the higher-pressure connection. Low side is the lower-pressure connection.
The main focus is identifying the high-side and low-side block valves from the tap locations before either valve is moved. In the field, the technician must read the tag, confirm the pressure reference and unit, check the process connection, and compare the instrument reading with the expected plant condition. The topic also links to calibration records, DCS scaling, alarm settings, and safe isolation before any instrument work.
A practical way to study this topic is to ask four questions: what pressure is being measured, what reference is used, how the signal reaches the DCS, and what failure would make the reading unsafe or misleading. This keeps the lesson tied to real maintenance and commissioning decisions rather than only theory.
Field examples
- On an orifice run the upstream tap is normally the high side. Closing it while the equalizing valve is shut can one-side the transmitter.
- Compare the local gauge, transmitter HART value, and DCS indication before deciding which value is credible.
- Record the unit, range, LRV, URV, and tag number before calibration or loop checking.
Common mistakes
- closing one block valve while the equalizing valve is shut and the other side is still at process pressure
- Trusting one reading without checking the pressure reference, unit, range, and process condition.
- Opening tubing, manifolds, or vents without proving isolation and zero stored pressure.
Safety
Follow plant SOP, PTW, isolation, depressurization, venting, draining, PPE, LOTO, and supervisor instructions before closing a block valve on a live pressure line.
Key takeaway
High-Side and Low-Side Block Valves helps a technician understand pressure readings, field installation, and safe troubleshooting. Always verify the unit, reference, range, and isolation state before acting on the measurement.
Imported study note from pressure_lesson_122. The app generates this text from a lesson seed. It is not a long textbook page.