Cleanroom differential pressure gauge: How to read and calibrate according to ISO standards

1. What is a cleanroom differential pressure gauge?

A cleanroom differential pressure gauge is a device used to measure the pressure difference between two areas - typically between a cleanroom and a corridor, or between two cleanrooms of different cleanliness levels.
This device ensures that airflow always moves from the cleaner area to the less clean area, preventing dust, microorganisms, or contaminants from flowing back.
It is an important monitoring tool that helps facilities maintain differential pressure in compliance with ISO 14644 and GMP standards.

Role in cleanroom pressure control

• Ensure compliance with international standards: ISO, GMP, and FDA require continuous monitoring of differential pressure.
• Prevent cross-contamination: positive pressure in pharmaceutical, food, and cosmetic production areas; negative pressure in hazardous chemical handling areas.
• Support audits and validation: data from differential pressure gauges serve as key evidence during quality assessments.
• Protect products and personnel: reduce the risk of product contamination and protect employees working with active substances or hazardous chemicals.

Common types of differential pressure gauges

• Analog differential pressure gauge (Magnehelic Gauge)
  Uses a Bourdon tube or diaphragm to measure pressure difference.
  Advantages: durable, low cost, easy to read.
  Disadvantages: difficult to integrate with digital monitoring systems.
• Digital differential pressure gauge
  Uses pressure sensors with digital display (LCD).
  Advantages: high accuracy, can connect to BMS/SCADA for remote monitoring.
  Disadvantages: higher cost, requires power supply.
• Dual needle differential pressure gauge
  Features two needles displaying the pressure of both areas simultaneously for easy comparison.
  Advantages: convenient monitoring, easy to detect abnormalities.
  Applications: often used in electronics cleanrooms and laboratories.

Applications in industries

• Pharmaceuticals: monitor positive pressure in compounding and packaging areas to prevent cross-contamination.
• Food: maintain clean conditions in processing and packaging lines to avoid microbial contamination.
• Electronics - semiconductors: control differential pressure in chip and component manufacturing cleanrooms to prevent micro-dust interference.
• Cosmetics: prevent dust and microorganisms in production areas, especially for skincare and makeup products requiring high purity.

2. Why is it necessary to control differential pressure according to ISO?

ISO 14644 and GMP requirements for cleanroom pressure
Under ISO 14644 and GMP-WHO standards, maintaining differential pressure is mandatory to:

• Maintain airflow direction: ensure that air moves from the cleaner area to the less clean area.
• Prevent cross-contamination: stop dust, microorganisms, or solvent vapors from entering the cleanroom.
• Support certification and audits: regulatory bodies (FDA, EU-GMP) always check differential pressure data when evaluating HVAC systems.

Facilities in pharmaceuticals, food, electronics, and cosmetics must prove that their differential pressure monitoring system operates continuously and reliably.

Risks of improper control
If differential pressure is not properly monitored and maintained, the following may occur:

• Product cross-contamination: dust or microorganisms may flow from ancillary rooms into the main production area.
• Audit non-compliance: may result in warnings, suspension, or loss of GMP/ISO certification.
• Safety risks for personnel: in hazardous chemical areas, failure to maintain negative pressure may cause leakage into the external environment.
• Economic losses: production batches may be discarded, leading to revalidation costs and loss of brand reputation.

Recommended differential pressure levels (Pa) by cleanliness classification

Note: The above values are recommended by ISO 14644 and GMP, and may be adjusted depending on HVAC design and product requirements.

See more: Latest price list of differential pressure gauges used in medical clean rooms

3. How to read a differential pressure gauge accurately

General principles when reading the gauge

• Identify the measurement unit: most gauges display in Pascal (Pa) or inch of water (inH₂O). 1 inH₂O ≈ 249 Pa, so conversion must be done correctly when comparing values.
• Observe the needle or digital display: analog gauges usually have a pointer, while digital gauges show numbers on an LCD screen.
• Compare with the calibrated scale: check where the pointer is on the scale and compare it with the required differential pressure value.

Checklist for reading the gauge
To avoid errors, operators should follow these steps:

1. Identify the pointer or displayed value
• For analog gauges: view directly to avoid parallax error.
• For digital gauges: check for flashing warnings or error codes.
2. Compare with the calibrated scale
• Check the pointer position on the scale (e.g., 0-60 Pa, 0-250 Pa).
• Ensure the correct unit is read (Pa or inH₂O).
3. Compare with the required differential pressure value
• Refer to ISO 14644 standards and internal SOPs.
• If the value is below the requirement → notify technical staff to check the HVAC system.

Practical example

• An ISO 8 cleanroom typically requires a differential pressure of ≥ 10-15 Pa compared to the corridor.
• If the gauge shows only 5 Pa, the system is not compliant, and dust or microorganisms may infiltrate the cleanroom.
• Conversely, if the differential pressure is too high (≥ 30 Pa), it may cause difficulty when opening/closing doors and affect operations.

See more: Digital Differential Pressure Gauge Installation: A Comprehensive Guide

4. Guidelines for calibrating a differential pressure gauge

Calibration frequency according to ISO/GMP

• Under ISO 14644 and GMP-WHO, differential pressure gauges must be calibrated periodically to ensure accuracy.
• Recommended cycle:
• Normally: every 6-12 months.
• In critical areas (aseptic pharmaceutical, microelectronics): every 3-6 months.
• Calibration results must be recorded in the equipment logbook for audit purposes.

Basic calibration method

1. Prepare equipment
• Use a reference manometer or pressure calibrator calibrated under ISO 17025.
• Check the condition of the differential pressure gauge before proceeding.
2. Zero adjustment
• Disconnect the pressure source, ensuring both ports are open to the same pressure.
• Adjust the pointer back to “0” on the scale.
3. Span adjustment
• Apply a reference pressure (e.g., 20 Pa, 50 Pa).
• Compare the gauge reading with the reference instrument.
• Adjust the span screw (if available) until the gauge matches the reference value.
4. Verification of results
• Record at least three calibration points (zero, mid-scale, and full scale).
• If the error exceeds the acceptable limit (±5% of full scale), the gauge must be repaired or replaced.

Checklist for safe calibration procedure

• Prepare an approved calibration SOP.
• Use reference equipment certified to ISO 17025.
• Place warning signs in the calibration area to prevent interruptions.
• Perform calibration in stable environmental conditions (temperature, humidity).
• Record calibration details: date, technician, reference equipment, results.
• Attach a calibration label to the gauge with calibration and expiry dates.

5. Common mistakes and how to fix them

During cleanroom operations, many facilities encounter issues when using differential pressure gauges. Below are the most common mistakes and their solutions:

Mistake 1: Installing the gauge in the wrong location

• Description: installed near doors, areas with strong airflow, or vibration sources → readings fluctuate and become unstable.
• Consequence: displayed values do not reflect the actual differential pressure between two rooms.
• Solution: install the gauge in a stable position, on the partition wall between the two areas being monitored, away from airflow and vibration sources.

Mistake 2: Not calibrating periodically

• Description: the gauge is used continuously but has not been calibrated for many years.
• Consequence: inaccurate readings, leading to cross-contamination risks or audit failure.
• Solution: establish a calibration schedule every 6-12 months, keep proper records, and attach calibration labels to each gauge.

Mistake 3: Confusing measurement units (Pa vs inH₂O)

• Description: many imported differential pressure gauges display in inch of water (inH₂O), while cleanrooms in Vietnam commonly use Pascal (Pa).
• Consequence: operators may compare values incorrectly against ISO/GMP standards, resulting in wrong decisions.
• Solution: train staff on unit conversion (1 inH₂O ≈ 249 Pa), clearly note the unit in SOPs and at the gauge installation site.

Overall solutions

• Develop a standard SOP for reading, recording, and verifying differential pressure.
• Establish a calibration and verification schedule with an ISO 17025 accredited provider.
• Conduct regular staff training to minimize operational errors.

See more: Unveiling the Significance of Differential Pressure Gauge in Pharmaceuticals Cleanrooms

6. Frequently Asked Questions

1: How often should a differential pressure gauge be calibrated?

Typically every 6-12 months, depending on GMP/ISO requirements and the criticality of the production area. For aseptic cleanrooms or electronics, it is recommended to shorten the cycle to 3-6 months.

2: Can calibration be done in-house, or is a specialized provider required?

Companies may perform basic checks, but for results to be audit-compliant, calibration should be carried out by an ISO 17025 accredited provider.

3: What is the minimum differential pressure required to prevent cross-contamination?

A safe minimum is usually 10-15 Pa between a cleanroom and a corridor. However, this value may vary depending on ISO 14644 cleanliness class and HVAC design.

4: Do digital differential pressure gauges need calibration like analog ones?

Yes. Although more accurate than analog types, digital sensors also drift over time. Both analog and digital gauges must be calibrated periodically to ensure reliability.

7. Contact for consultation & calibration services

Do you need a cleanroom differential pressure gauge compliant with ISO/GMP or a regular calibration service? Let VCR support you:

• Supply of genuine differential pressure gauges (Magnehelic, digital, dual needle, etc.)
• ISO 17025 calibration services, with documentation valid for GMP/ISO/FDA audits
• Integrated HVAC & cleanroom monitoring solutions for pharmaceuticals, food, electronics, and cosmetics

Contact us today for free consultation and to receive a detailed quotation:

• Schedule a consultation with VCR experts
• View the latest calibration price list

With more than 10 years of experience in cleanroom equipment, VCR is committed to delivering optimal solutions - cost-effective - internationally compliant.

Hotline: 090.123.9008
Email: [email protected]
Website: https://donghochenhap.com/

Diep VCR