No. Let me say that again: no. A gate valve is made for only two positions, fully open or fully closed. Do not ever try to use it as a throttle.

Why is that so bad? When you leave a gate valve partly open, the wedge sits right in the flow path. The fluid speeds up and starts eroding the sealing surfaces. That erosion has a name: wire drawing. Once the seat is damaged, the valve will leak internally and eventually fail completely.

There is another problem. A partially open gate valve vibrates. The wedge bangs against the seats every time the flow changes. That causes mechanical damage to both the wedge and the seats.

So if you need to adjust flow, use a globe valve or a ball valve with a V port trim. And make sure everyone on your operations team knows this rule. It will save you from replacing gate valves way ahead of time.

You need to answer four questions about your fluid. What is in it? How hot is it? How much pressure? Is it corrosive?

For ordinary oil, gas, and steam at high pressure and high temperature, carbon steel is your standard choice for the valve body.

If the fluid is corrosive, for example acids, seawater, or chemical solvents, you need stainless steel. CF8 or CF8M are common picks.

For really nasty corrosive conditions, or for temperatures above 550 degrees Celsius, or for cryogenic services down to minus 196 degrees, move up to alloy steels or special corrosion resistant alloys.

Now do not forget the trim. The trim means seat rings, stem, and disc. I have seen people pick a good body but cheap trim, and then the valve fails early. For clean water, an iron body with bronze trim is fine. But if your fluid has sand or other abrasive particles, you must specify hardened trim. Stellite overlay on the seats and disc will stop scoring and keep the valve tight for many years.

The big difference is how they seal. A wedge gate valve uses a tapered disc. The stem pushes it down into the seat, and the sealing force comes from that stem thrust. That works fine for oil, gas, and water at normal temperatures. A parallel slide gate valve uses two flat discs with a spring in between. When you close it, the line pressure pushes the downstream disc against its seat. The higher the pressure, the tighter the seal. So why does that matter? Because a parallel slide valve never gets thermal binding. If you have superheated steam above 400 degrees Celsius, or your system goes through a lot of heating and cooling cycles, the parallel slide design is much safer. The downside is cost. Wedge valves are cheaper and easier to fix. Parallel slide valves cost more, but they perform better at high temperatures.

I have seen gate valves fail in four typical ways.

First, leakage around the stem. The packing wears out from frequent operation, high pressure, or chemical attack. Check the packing gland once in a while and tighten it if it feels loose.

Second, leakage through the seat. That usually means the seat or the gate is damaged. High velocity flow, debris caught between the surfaces, or long term corrosion are the usual suspects. Do not use a gate valve for throttling, and try to keep the fluid clean.

Third, the stem snaps. This often happens because someone over torqued the valve, or because of corrosion in a salty environment, or metal fatigue from too many cycles. Use a torque wrench on large valves and lubricate the stem threads on rising stem designs.

Fourth, the gate gets stuck. Sediment builds up inside the valve body, especially in slurry service. Or the valve was installed crooked. The simple fix: cycle any valve that sits unused for a long time, and flush the line before you close it.

Here is the simple version. A full port gate valve has an opening that matches the inside diameter of your pipe. Fluid flows through as if the valve was not even there. Pressure drop is almost nothing, and you can send a pipeline pig right through for cleaning or inspection. A standard port valve has a smaller opening. That adds friction and you lose some pressure. You also cannot pass a pig. So when does it matter? If you are running a long transmission line, or your system is already close to its pressure limit, spend the extra money on full port. But if you just need an isolation valve on a process line, and you do not care about a little pressure drop and you never use pigs, a standard port valve will save you cash.

A rising stem valve, or OS&Y, literally moves the stem up when you open it. You can stand ten meters away and tell whether it is open or closed just by looking at how much stem is sticking out. The threads are outside the valve body, so they never touch the fluid. That means less corrosion and you can grease them easily. A non rising stem valve keeps the stem at the same height. You have to look at a separate indicator to know the position. Its threads are inside the valve, right in the fluid. Over time that leads to corrosion, dirt buildup, and wear. When would you use each one? For refineries, power plants, and any aboveground piping, rising stem is the standard. Fire protection systems require rising stem by NFPA rules. Non rising stem is for underground pits, spots with low headroom, and waterworks that follow AWWA standards.

Start with the metal seated type. It loves high temperatures, often over 400 degrees Celsius, and it handles abrasive fluids well. The problem shows up when your fluid contains sand or small pebbles. Those hard particles slowly grind down the metal sealing surfaces, and eventually you get leakage. Now look at the resilient seated valve. It uses a rubber lining that actually molds itself around small solid particles. That means a tight shutoff even if the fluid is a bit dirty. The downside is temperature. You usually cannot go above 70 degrees Celsius with a resilient seated valve. So which one do you pick? For clean fluids at room temperature or moderate heat where zero leakage is a must, go with resilient seated. For high temperature, high pressure, or fluids full of grit, choose metal seated. And one more thing: make sure the metal seating surfaces are hardened, for example with Stellite. That makes a big difference in how long the valve lasts.

The main standards you will encounter are API 600, API 6D, API 603, and ISO 10434. In practice, ISO 10434 is essentially equivalent to API 600 – both cover cast steel gate valves for refinery and chemical plant services. API 6D, on the other hand, is specifically tailored for long-distance pipeline applications, with added emphasis on double block & bleed (DB&B) and in-line sealing integrity. API 603 applies exclusively to stainless steel valves, suitable for Class 150~300 services involving corrosive media.

How to choose?

• If your application requires pigging or double isolation, API 6D is the preferred choice.

• If you prioritise shell safety under high temperature/pressure and full material traceability (typical in refinery duties), go with API 600.

• For small-bore forged steel valves, refer to API 602.

Important note: All these standards reference ASME B16.34 (pressure‑temperature ratings), ASME B16.10 (face‑to‑face dimensions), and ASME B16.5/B16.47 (flange dimensions). However, each standard imposes its own additional requirements on shell wall thickness, leakage testing, and NDE procedures. If you are unsure which standard fits your specific service conditions, feel free to contact us – we offer free, tailored selection advice for your actual operating conditions.