Can You Install Differential Pressure Gauges in Pharmaceutical Cleanrooms?

Pharmaceutical cleanrooms generally use 0–60 Pa micro differential pressure gauges.
It is not recommended to select red-oil type differential pressure gauges.

Main Uses of Differential Pressure Gauges

Air differential pressure gauges are suitable for measuring small air pressure differences. They are widely used in pharmaceutical and microelectronics industries to display and monitor environmental pressure differences.
They can be installed by embedding or wall mounting on the outside wall of a cleanroom. No power supply is required. They offer high sensitivity and relatively high measurement accuracy.

For pressure measurement:
Connect the pressure source to any one of the two high-pressure ports with a tube and block the unused one. Allow one or both low-pressure ports to be open to the atmosphere.

For differential pressure measurement:
Connect the high-pressure source to any one of the high-pressure ports with a tube, and connect the low-pressure source to any one of the low-pressure ports with a tube. Block the two unused pressure ports on the gauge.

For negative pressure measurement:
Connect the pressure source to any one of the low-pressure ports with a tube and block the unused one. Allow one or both high-pressure ports to be open to the atmosphere.

Installation of Differential Pressure Gauges

A 2 mm thick 304 stainless steel mounting panel can be selected for installation. After installation, there are no exposed components, ensuring a neat appearance and convenient installation and maintenance.

Differential pressure is usually monitored between cleanrooms and non-cleanrooms. The installation position is generally on the wall between the cleanroom and the non-cleanroom area, so that the pressure difference between inside and outside the cleanroom can be observed from outside.

For red-oil type differential pressure gauges, horizontal installation is required.
For pointer-type differential pressure gauges, zero calibration must be performed.

Attention must also be paid to the tubing connection direction:
The high-pressure tube must be connected to the high-pressure room, and the low-pressure tube must be connected to the low-pressure room.

If the cleanroom is a positive pressure room, connect the high-pressure port of the gauge to the cleanroom and leave the low-pressure port unconnected.
If the cleanroom is a negative pressure room, connect the low-pressure port of the gauge to the cleanroom and leave the high-pressure port unconnected.

Installation Procedure for Red-Oil Differential Pressure Gauges

The installation must be performed in a specific sequence. Improper installation may result in malfunction.

Step 1: Fix the gauge in position.
There are two mounting holes on the gauge. Use screws to install it on the wall or on a vertical surface.

Step 2: Adjust the horizontal position so that the bubble inside the level indicator is centered.

Step 3: Loosen the zero adjustment knob by 3–4 turns and mark the number of turns.

Step 4: Fill the gauge with red oil.
Remove the filling plug and pour red oil into the filling hole until the liquid reaches the zero scale, then tighten the plug.

Step 5: Fine adjustment for zero calibration.
After the red oil stabilizes, under atmospheric pressure conditions, adjust the zero knob so that the zero mark aligns with the red oil liquid level.

Step 6: Connect the hoses.
Connect the high-pressure and low-pressure hoses to the corresponding “High” and “Low” ports on the gauge. Installation is now complete.

Installation Procedure for Pointer-Type Differential Pressure Gauges

1. The instrument should be installed vertically relative to the horizontal plane of the cleanroom project.
2. The measurement point and the installation position should be at the same height, otherwise additional height error correction must be considered.
3. The distance between the measurement point and the instrument should be as short as possible to avoid slow indication.
4. Ensure airtightness and prevent leakage.
5. New pressure measuring instruments must be calibrated before installation and use to prevent loss of accuracy caused by vibration, damage during transport, or other factors.

Where Should Differential Pressure Gauges Be Installed?

The installation of differential pressure gauges mainly depends on two factors: when they are required and how they should be arranged.

In addition to rooms and equipment with explicit pressure difference requirements, process requirements must also be considered. From the perspective of cost and management, the number of gauges should be minimized. Generally, gauges should be installed in lower-grade areas, while pressure tubing should be installed in higher-grade areas.

Typical locations include:
between filling rooms and corridors,
between clean areas and general areas,
and between higher-grade and lower-grade clean areas.

Installation Notes

Any location with different cleanliness levels where cross-contamination must be prevented should be equipped with differential pressure gauges.
In general, locations where airflow exists between clean and non-clean areas, or between areas of different cleanliness levels, must be equipped with pressure indication devices, such as conveyor openings.

Differential pressure gauges should also be installed on both sides of pre-filters and medium-efficiency filters in air-conditioning systems to detect filter integrity.

Excessive pressure differences should be avoided to reduce energy consumption.
For example, in engineering practice, the recommended pressure difference for Grade A areas is about 60 Pa and should not exceed 100 Pa.
Pressure adjustment should start from the innermost room (the highest cleanliness level) and gradually decrease outward.

It is not recommended to install differential pressure gauges on pass boxes between different cleanliness levels. Pass boxes should be treated as airlocks and equipped with laminar airflow. Installing pressure gauges on pass boxes has no practical significance because the doors on both sides cannot be opened simultaneously and no airflow occurs. Therefore, pressure indication devices are not necessary. However, regular inspection and maintenance should be carried out to ensure airtightness.

Aseptic filling rooms facing general-area corridors should be equipped with pressure indication devices and monitored.

Conclusion

Design, construction, and commissioning are the three key factors ensuring correct pressure differentials in cleanroom systems. Through commissioning, problems in pressure control can be identified and design solutions can be improved, construction operations standardized, and failures avoided.

Pressure control and the installation and commissioning of differential pressure gauges are essential and necessary measures to ensure that cleanroom pressure differentials and cleanliness levels meet the required standards.