Where are the ULPA differential pressure measuring points located?

This problem seems to be a detail of the pipeline layout, but the actual impact is greater than imagined.

The location of the measuring point determines what you are measuring. For the same filter, the pressure tap is placed before and after the filter element to measure the pressure difference of the filter element; if it is set at the inlet and outlet of the box, it will measure the pressure difference of the whole machine; if it is set at both ends of the air duct, it will measure the system pressure difference. The three numbers may differ quite a bit and have completely different uses.

Disputes that often arise on site - 'Why is the pressure difference so much higher than what is reported?' 'Which value should be used to judge replacement?' - are often rooted in inconsistent definitions of measuring points.

First figure out which object is being measured

The first step in measuring differential pressure measurement points is to clarify the evaluation objects.

Filter body pressure difference. The pressure ports are located on the air inlet and outlet sides of the filter element, close to the front and rear of the filter element. This data reflects the actual dust accumulation status of the filter material and edge sealing, and is the main basis for judging whether the filter element needs to be replaced.

Pressure difference in the filter section. The pressure port is located at the inlet and outlet of the filter section, including the filter element, installation frame and box of this section. This data is used to evaluate the overall resistance of the filter section and is commonly used in system design.

Pressure difference across the entire machine. The pressure port is located at the air inlet and outlet of the unit, including the fan, filter, internal channel of the box and diffusion structure. This data reflects the overall working status of the unit and is used to determine whether the fan is normal.

The relationship between the three is: pressure difference of the whole machine > pressure difference of the filter section > pressure difference of the filter element body. Because the latter is included in the former. Comparing the pressure difference of the whole machine with the resistance curve of the filter element, the number is naturally higher - this is not a product problem, but a different definition of measuring points. For specific troubleshooting ideas, please refer to the relevant instructions on initial resistance anomalies.

How to arrange the pressure port

After determining the evaluation object, the location and direction of the pressure port are also important.

Avoid local high-speed airflow. If the pressure tapping port is located in an area where the air flow velocity is high or the direction changes suddenly, the reading may be affected by dynamic pressure. The pressure tapping port should be set at a position where the air flow is relatively stable and the direction is perpendicular to the pipe wall. Air duct elbows, diameter reduction points and near valves are usually not suitable for direct pressure taking.

The high and low voltage sides must correspond. The pressure port is divided into high-pressure side and low-pressure side, and the two ends should correspond to the air inlet side and air outlet side of the filter respectively. If the connection is reversed, the reading will show a negative value or an abnormally low value.

The pressure port cannot extend into the air flow. The nozzle should be flush with the inner wall and not protrude into the airflow channel. The protruding nozzle will cause local turbulence and may also be blocked by dust.

The pipeline must be sealed and unobstructed. Air leakage at the connection of the pressure pipe, pipe bends or water accumulation will cause the reading to deviate from the actual value. When the internal space of the equipment is compact, the pipeline layout should leave room for inspection to facilitate subsequent maintenance.

When two or more filters share a set of differential pressure gauges, the positions of the pressure ports must be consistent. If one takes the pressure difference of the filter element and the other takes the pressure difference of the whole machine, the values ​​on the table are not comparable. involving HEPA/ULPA air filter products of different grades have the same pressure measurement principles.

Special considerations for pressure sensing within equipment

Device-side applications such as The EFU equipment-side fan filter unit has a compact internal space, and there are several additional points to pay attention to in the pressure pickup arrangement.

The location of the pressure port is limited by the structure. There may be mechanical arms, cables, and transmission parts inside the equipment. The pressure port should be kept away from these moving parts to avoid interference or wear.

The direction of the pipeline must be planned. If the internal pipelines of the equipment are laid randomly, they may affect the movement of other components or be pulled during maintenance. It is recommended that pressure piping be included in the layout during the equipment design stage.

Appropriate piping materials must be selected for high temperature, high humidity or vibration environments. Ordinary plastic hoses may deform under high temperatures and may become loose in a vibrating environment. The specific material selection is confirmed according to the equipment working conditions.

Equipment operating status can affect readings. Equipment starting and stopping, mode switching, and mechanical movement may affect local airflow. When measuring, make sure the equipment is in stable operating condition and record the working conditions at that time. Supporting The FFU fan filter unit system, unit gear and operating mode must also be recorded.

Common misconfigurations

In actual projects, the following pressure sensing settings can easily cause data misreading.

The pressure port is located near the sealing surface of the filter element. The airflow at this location may be affected by the sealing structure, and the reading cannot accurately reflect the resistance of the filter element body.

The distance between the pressure ports on the high and low pressure sides is too close. If the two ends are too close, the local pressure difference may be measured instead of the pressure difference before and after the filter.

The pipelines are incorrectly connected or unclearly marked. When multiple devices share a set of differential pressure gauges, if the pipelines are connected incorrectly or are unclearly labeled, the corresponding readings will be confused. It is recommended to check each device after installation.

The measurement point definition is not written into the file. If there is no clear pressure location in procurement documents, drawings and maintenance ledgers, the data read by different people may correspond to different objects. Subsequent comparisons and analyzes will be affected. For measuring point definitions and system verification methods, please refer to the relevant instructions on differential pressure measuring points and system verification.

Project judgment example

The ULPA differential pressure gauge of a certain equipment read too high, and the operation and maintenance team suspected that the filter element was clogged. Comparing the readings with the product curve, we found that the initial resistance was nearly twice as high as the air volume.

The investigation found that the pressure tapping port of the differential pressure gauge is located at the inlet and outlet of the unit. It measures the pressure difference of the entire machine, including the resistance of the fan section and the internal structure of the box. The comparison product curve is the resistance of the filter element body. The two are not measuring the same object.

Adjust the pressure port to the front and rear of the filter element. After re-measurement, the reading is about 220 Pa, which is basically consistent with the initial resistance data under this air volume, indicating that the filter element is in normal condition.

The key to this case is: first confirm the measurement point definition, and then determine whether the data is abnormal. If the measuring point is wrong, there will be no basis for judgment. involving ULPA ultra high efficiency filter or To judge the resistance of HEPA high-efficiency filter , you must first check the measuring points.