Why is the diameter of the inlet pipe of a safety valve always smaller than that of the outlet pipe? Thank you

The outlet diameter of the safety valve should be 1 (for slightly open valves) to 2 sizes larger than the inlet diameter; it should also have as few bends as possible and be securely fixed. This is done primarily to ensure effective pressure relief. I would appreciate any advice from those with more experience.

The inlet pressure is high and the outlet pressure is low, so the outlet must be larger than the inlet.

High inlet pressure, low actual flow rate； The outlet pressure is low and the actual flow rate is high, so the outlet is larger than the inlet.

It mainly depends on the calculations for the safety valve; the selection is determined by the manufacturer of the safety valve. Once the safety valve activates, the pressure decreases, and the volume of gas increases by many times. The decrease in liquid pressure and the flow rate are also factors that need to be taken into account. Additionally, this is done to reduce vibrations and other issues In fact, selecting a safety valve involves choosing a specific model; sometimes the discharge capacity can vary quite significantly. Yet it is still necessary to choose the same model. The most important thing in the design process is to calculate the discharge capacity accurately. For the actual selection, it’s best to consult the safety valve manufacturers – we can use their software to carry out the calculations first, although there might be fewer factors taken into consideration

It’s not necessarily the case; there are also ones with the same size for import and export. What was said upstairs is correct – the discharge volume is calculated by the safety valve manufacturer, who then determines the appropriate model based on the characteristics of that safety valve.

Not necessarily. For gas release, full-open safety valves are used; such valves generally have an inlet diameter that is smaller than the outlet diameter, and this is because the pressure before the valve is much higher than the pressure after it, resulting in significant changes in the volume of gas as pressure changes. For liquid discharge, slightly opening safety valves are generally used; these types of safety valves usually have the same inlet and outlet, as the volume of the liquid changes very little with pressure. This post was last edited by processimu on 2008-1-9 12:59 ]

Agree with the view from the 7th floor; the explanation is easy to understand. Thank you

Hmm, that makes sense: handshake

The large outlet size is mainly intended to reduce pressure. There’s nothing special to say about direct discharge, but when dealing with hazardous materials that require a treatment system, reducing pressure can lessen the stress on the system and help maintain its stability

The inlet and outlet sizes of the relief valve can be similar. Since the volume of the gas increases after pressure reduction, the outlet diameter also needs to be large

That’s right; when the outlet pressure is low, the gas needs to expand, which requires a larger diameter for the outlet pipe! I agree with what was said on floor 7! The liquid discharge can be the same! The process requires calculating the discharge volume; to select a safety valve, one can turn to manufacturers. A larger outlet on the safety valve will make the system more stable, as the flow rate is reduced significantly in this way. But it’s not the case that the larger, the better

Generally, the diameter of the inlet and outlet pipes for a connected safety valve is larger than that of the valve’s own inlet and outlet ports; the resistance in the inlet pipe should not exceed 3% of the set pressure, while the resistance in the outlet pipe should not exceed 10% of the set pressure. The pipe diameter can be recalculated based on this.

I don’t understand either; I came in to take a look. I’ve learned something new, thank you to everyone up there!

A typical pressure reduction setup, with a small inlet and a large outlet to create a pressure reduction buffer

I’ve encountered a situation like this; I’d appreciate it if experts could help analyze it: the diameter of the inlet pipeline for the safety valve is larger than that of the valve’s inlet, so a size reduction is required in order to make the connection. I’m wondering whether this will have any impact on pressure relief

I/ Process for selecting a safety valve: 1. Determine the discharge area of the safety valve based on its discharge capacity. 2. Select the appropriate model of safety valve and determine the diameters of the inlet and outlet pipes. 3. For the selected model of safety valve, the diameter of the outlet pipe is usually larger than that of the inlet pipe. II: Calculating the DN of the inlet and outlet pipes of the safety valve: 1. Determine the diameter of the inlet pipe based on the volumetric flow rate and maximum flow velocity at the inlet. 2. Determine the diameter of the outlet pipe based on the volumetric flow rate and maximum flow velocity at the outlet. 3. Since the inlet pressure is higher than the outlet pressure, the density of the material at the inlet is necessarily greater than that at the outlet; therefore, the volumetric flow rate at the inlet is lower than that at the outlet, meaning the diameter of the inlet pipe must be smaller than that of the outlet pipe. (1) If it is gas discharge, follow the steps mentioned above for calculations. (2) For liquid safety valves, it depends on the type of fluid involved; if it is a light hydrocarbon liquid, the diameter of the outlet pipe will be much larger than that of the inlet pipe, mainly because the fluid vaporizes after being discharged through the safety valve. (3) In the case of liquid safety valves, if there is no phase change between the inlet and outlet, then the diameters of these pipes should be the same. Another reason for a larger diameter at the outlet of the safety valve is that the back pressure behind the safety valve is generally low. If it discharges directly into the atmosphere, the back pressure is 0.1 MPaA; if it discharges into a flare system, the back pressure is typically designed to be 0.2 MPaA. This post was last edited by 1681818 on 2008-1-18 at 20:48

The terms \"full opening\" or \"slight opening\" for safety valves are terms used in China; it seems that such expressions aren’t used abroad.:)

What was said upstairs is correct; according to ASME standards, the safety valves we usually refer to are classified into three types: safety valves, safety pressure relief valves, and pressure relief valves. The pressure relief valve is what we call a slightly opening type safety valve. The safety valve as we commonly use it should be referred to as a safety pressure relief valve according to ASME standards, and the safety valve as defined by ASME specifically refers to devices used for pressure relief in steam and gas applications.