OK, so you’ve settled on the kind of valve you need, but that’s not the material question, is it?
Question No. 2: What should the ball valve be made of?
At first blush, this may not seem like an important question. A valve’s a valve, so long as it does what it’s supposed to, right?
Well, maybe. Or maybe, if you are a food processor, you slowly give your customers lead poisoning. I mean, who’s going to buy your burritos if all your customers are dead?
Brass or Stainless Steel? These are just two of the choices available to you when choosing valves.
That is, of course, a wild exaggeration, but lead leakage from brass valves make them less desirable in some industries than others. And while plastic valves can be a good choice in many situation, their lower burst pressures can rule them out of some uses.
As with the previous discussion, we will be talking about a few major categories of materials. Although valves can be made out of pretty much anything, this should give you a good starting point, from which you can go on to do some serious research, including industry regulations (e.g. fire ratings and specific bans, such as the need for lead-free products), pressure ratings and media compatibility regarding which valve material works best with which media. We will post a compatibility chart soon for you to see.
PVC and other plastics
Plastics don’t corrode like metal valves, making them a leading material in some industries. Although there is a wide variety of plastics available, the most commonly used is polyvinyl chloride (PVC), which is resistant to water and chemicals, including acids.
Because the valves do not rust, they don’t jam as easily, freezing the valve open or closed. Likewise, the valves are less likely to acquire as much buildup as metal valves, meaning less blockage of pipes and better flow rates for a longer period. This makes them good for industries where other piping and valves would need to be replaced regularly – although, as we will see later, other materials have strong corrosion resistance and other benefits.
Plastic valves tend to be easier to install than metal valves, at least when it comes to physical labor. Plastic valves can be installed with hand tightening, plus a quarter-turn with a strap wrench. Compare that with the way metal valves are secured – that is, with as much force as you and your three best workers can muster.
In fact, tightening the valves/piping too much can be a concern. Some experts say that plastic valve failures can be traced back to overzealous installers who put too much stress on the part when installing it.
Another prime advantage of plastic valves is cost. Usually less expensive than brass or steel, plastic valves are also somewhat lighter than metal valves. That makes them cheaper to transport, adding to the savings.
Where metal valves have an advantage over plastic ones is temperature and pressure. As temperatures rise, pressure ratings fall. That is true with all piping and valves. Plastic valves can serve admirably in many situations, but high temperature and high pressure applications often require a different material. PVC Grade 1 Type 1 has a pressure rating of about 150 psi at 75°. The maximum safe temperature for PVC is around 140°, at which point the pressure rating drops to just more than 30 psi. That is, of course, dependent on the chemicals being pumped through. Different media would affect the piping/valves differently.
Valves made from other plastics, such as Kynar and Teflon (PTFE), have higher pressure and temperature ratings. Kynar valves are rated up to 230 psi and Teflon valves can withstand temperatures up to 300°. Other plastics work under extremely heavy pressure, but you will pay just as heavily for the material.
And if you are paying more, then you might want to move up the materials chain to check out brass valves.
Brass and Bronze Valves
Brass and bronze are both copper alloys, which makes them stronger than plastics, generally speaking, with a mid-range price. They are the next step up in terms of pressure and temperature ratings, although they are not the top end.
Brass is primarily a mixture of copper and zinc, although other metals may be added to give it different properties, including corrosion resistance (more on that later). Brass is considered one of the softer metals used for industrial valves, but the valves are rated higher than most plastics. You may find special cases where brass valves are rated higher, but most top out at around 600 psi.
A mixture of copper and tin, bronze is a harder and more brittle metal than brass. It has similar pressure ratings to its brass counterparts.
Brass and bronze both show high resistance to corrosion, with bronze performing especially strong against saltwater corrosion. Brass can go through a process called dezincification, in which the zinc in the part seeps out over time, leaving the copper superstructure which can become brittle and cause failure. Brass is more susceptible to that process in certain areas of the country, including areas of Texas, the Carolinas and Missouri. That said, brass usually has a comparable service life to bronze in most cases.
Brass and bronze both respond better to higher temperatures than plastics because of their ability to absorb more heat. Both are good conductors, which makes them more efficient in plumbing systems. Brass piping and fittings are often prized in home plumbing because of the way the material balances malleability and high temperatures.
Because of their chemical make up, both types of valves also accept solder and welding better than some other metals like stainless steel, which often must be abraded before welding to break down the oxide layer on its surface.
Unfortunately, for all of the good things that brass valves have going for them, there is a drawback. Lead is often added in low levels to harden the alloys and assist in their machinability. Although the addition of lead is minimal – often less than 2% - and the likelihood of contracting lead poisoning extremely rare, the use of brass valves, fitting and piping can be a concern for people who manufacture foods and drinks.
In some cases, lead can leak into the materials being transported. Therefore, the Food and Drug Administration (FDA) does not approve of brass valves being used. California has gone so far as to eliminate brass materials with lead content higher than 0.25% when they come into contact with a wetted surface.
Lead-free brass is a substitute, where silicone is used instead of lead. DirectMaterial.com manufacturing partner, DuraChoice, recently introduced a new line of lead-free brass valves, which are UL and CSA certified. Because of the different manufacturing process, those parts are more expensive than normal brass valves.
And if you are going to pay more, you might want to consider the next level of valve material – steel and stainless steel.
Carbon Steel and Stainless Steel
Steel is a very hard metal, which contributes to its resilience. The valves are not going to take damage like brass will, meaning they should resist leaks better over time.
Likewise, they have a wider working temperature range, giving them more versatility. Add that to a longer life cycle and, even though they cost more than brass, you could save more over time.
Like virtually every other part of this article, though, let me say “steel” has too many types to make a lot of blanket statements about it. However, we can talk about a couple of popular types – carbon and stainless steel.
Carbon steel (also known as “mild steel”) is a mix of iron and carbon, although some other alloying elements may be used to harden the steel and give it greater corrosion resistance. And that is the main difference between carbon and stainless steel.
We can talk about various hardness levels and ferromagnetism, but without special treatment, carbon steel is more likely to rust than stainless steel and that can mean a shorter service life.
That is not to say those valves are not useful. Carbon steel valves can be used in many instances where pressure and temperature extremes make other materials unusable. DirectMaterial.com sells carbon steel valves pressure rated up to 6,000 psi and has added corrosion resistance thanks to its material make up.
If you are looking for the top of the line in pressure ratings, high temperature functionality and corrosion resistance, though, you probably want to go with stainless steel. Stainless steels are iron alloys with chromium and nickel. Their chemical make up makes them highly corrosion resistant and particularly strong. The 6,000 psi valves mentioned above also come in Stainless Steel 316. Here’s an article about both types of high pressure valve.
What’s with the “316” you ask? That is the type of stainless steel. It is extremely corrosion resistant thanks to higher levels of nickel and the addition of molybdenum. The three metals work in concert to make the valves much more resistant to chlorides. Stainless steel 316 is often used in fast moving marine environments, as well as food production. In fact, Stainless Steel 316, 304 and 302 are all FDA approved for food and beverage handling.
Here is an article about the differences between SS316 and SS304, two of the more popular types of stainless steel for valve manufacturing.
To sum up, you should look at considerations like industry and environment as well as price when picking the right valve for your project. Take a look at the bottom line, but consider the factors that could affect it.
You don’t want to pay more than you have to, but if you invest in pipes that you will constantly need to replace, necessitating downtime, that is going to hurt you in the long run. The same goes for buying products that could hurt production or your customers. Look at the different kinds of material on this list to narrow your search, then seek out a little more information on a specific material if it looks like it fits your needs.
Next up, we’ll talk about sizing, flow rate and other considerations.