Working Pressure vs Design Pressure in Industrial Filter Housings

In the process of filter inquiry and selection, the "working pressure" and "design pressure" on the nameplate and parameter table are often confused and even regarded as the same concept - this is a serious cognitive misunderstanding! The difference between the two is directly related to production safety and procurement costs.

Working Pressure: Refers to the actual pressure that the filter bears internally for a long time under normal and continuous operating conditions. Design Pressure: Refers to the maximum pressure limit that the filter shell and its pressure-bearing components can safely withstand during design and manufacturing, serving as the safety boundary of the equipment. Design pressure is the safety upper limit for filter design, while working pressure is the real-time pressure during actual operation. Therefore, design pressure must be higher than working pressure (including all possible peak values of pressure fluctuations).

For example: On the pressure gauge of the filter, the 0.8 MPa that the needle currently points to steadily is the actual pressure the equipment bears during daily operation - this is the operating pressure. The 1 MPa at the far right end of the gauge scale, marked as the upper limit, corresponds to the design pressure (safety limit) that the filter housing can withstand.

In daily operation, you should keep the needle within the operating pressure range around 0.8 MPa for long periods, and avoid constantly letting it approach the 1 MPa design pressure red line. However, this 1 MPa upper limit exists to handle occasional transient pressure surges in the system, ensuring the equipment remains safe under such circumstances.

In the design process of Industrial Filter Housings, engineers usually reserve a certain safety margin on the basis of working pressure. In engineering practice, this safety factor commonly ranges from 1.25 to 1.5. The specific value shall be determined comprehensively based on operating conditions, design specifications and material properties. Therefore, design pressure is not simply equivalent to working pressure. Instead, it is a safety upper limit determined by fully considering factors such as pressure fluctuations, temperature effects, material fatigue and corrosion allowance. It is equivalent to a "buffer zone" or "safety guarantee" reserved for equipment operation.

Why is design pressure a must-have?

1. Water Hammer Impact (Pressure Fluctuation)

Sudden start/stop of water pumps or rapid valve closure will generate an instantaneous pressure peak in the pipeline, which may be much higher than the normal working pressure. Without the safety margin provided by design pressure, the filter shell could be directly ruptured by this "shock wave".

Therefore, the structural strength of the filter shell is particularly critical in high-pressure systems or those with frequent start/stop cycles. For instance, design measures such as the one-piece reinforced structure of PPH Filter Housings or PVDF Filter Housings and thickened key pressure-bearing parts can effectively reduce the risk of structural deformation under transient overpressure conditions.

2. Instrument Malfunction or Misoperation

If the upstream pressure regulating valve or the pump outlet pressure controller malfunctions, causing the system pressure to rise continuously, design pressure will act as the final "brake" to ensure the equipment can withstand overpressure until the safety valve lifts to release pressure.

3. Pressure Rise Caused by Temperature Increase

In a closed system, liquid expansion due to temperature rise will lead to a sharp pressure surge. Design pressure must be able to accommodate such potential temperature-induced pressure effects.

So how to correctly select the design pressure of a filter?

1. Verify the Filter's “Design Pressure”: Ensure that the design pressure of the selected filter is ≥ the maximum possible pressure.

2. Determine the “Working Pressure”: Check the normal and stable operating pressure of the process flow in MPa - this is the starting point for filter selection.

3. Evaluate the “Maximum Possible Pressure”: Consider extreme scenarios such as the aforementioned water hammer and instrument malfunction, and estimate the maximum instantaneous pressure that may occur in the system.

In practical projects, when the system working pressure ranges from 0.6 - 1.0 MPa, the design pressure of stainless steel filters is usually set at 10 bar (standard type) or 13 bar (reinforced type). This design range can effectively cover water hammer impacts, pump start-stop cycles and instantaneous pressure peaks. There is no need to blindly pursue a higher design pressure, thus avoiding unnecessary cost increases. For common applications, you can refer to our standard Stainless Steel Filter Housing with a 10 bar design pressure.

Working pressure and design pressure are like the “gentle reminder” and “firm safety line” of a filter. One tells us how to ensure smooth daily operation, while the other teaches us how to guard against unexpected risks. When selecting a filter, please develop a good habit: not only ask “What is its working pressure?” but also firmly ask “What is its design pressure?”