Brass Ball Valve Markings: What 600 WOG Really Means

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There is a number stamped into the side of almost every brass or bronze ball valve in your house, and it is a big one. 600 WOG. Sometimes a second number sits under it — 150 SWP — and sometimes the letters read CWP instead. Homeowners see 600 and assume they have bought something heroic. Apprentices see 150 and wonder why it dropped.

Quick answer from a licensed plumber: the two numbers are ratings for two completely different jobs. 600 WOG is the valve’s pressure limit for water, oil or gas at ordinary room temperature, with no pressure spikes. 150 SWP is its limit on saturated steam, which is hot, and that is the entire reason it is a quarter of the other number. Neither one is a quality score, and on a house running 40 to 60 psi, both are so far above your working pressure that the marking should not decide which valve you buy. What should decide it is on the back of the data sheet: whether the valve is rated for drinking water at all.

At a glance

What the three letters actually stand for

WOG is not an engineering unit. It is an abbreviation of the three media the rating applies to. Boshart’s technical knowledge base states it plainly: “WOG stands for Water Oil Gas and is used to indicate the pressure rating of valves and fittings.” The same page defines the rating itself as a “General ‘Non-Shock’ pressure rating indicating the maximum PSI for the medias water, oil or gaseous.”

Two words in that sentence carry all the weight. Non-shock. And, as the same page puts it, “The real meaning of WOG remains ‘ambient temperature fluids’.” So the number on the valve body describes a valve sitting at room temperature with steady pressure behind it. That is the laboratory condition. Your house is not always that.

The manufacturers do not agree on the vocabulary, and that tells you something

This is the part that surprises people, and I only found it by opening the data sheets rather than trusting the castings.

Milwaukee Valve’s specification sheet for its BA-100 bronze ball valve prints the rating exactly the way the valve body does: 600 WOG/150 SWP. The drawing on that sheet even shows the lettering cast into the side of the valve.

Now open the equivalent sheet from Apollo, one of the most widely installed bronze ball valves in America. Its 70-100 series data sheet has a box headed “performance rating” with four columns: CWP, SWP, temperature, vacuum service. The figures underneath are 600 psig, 150 psig, 500°F (maximum temperature), 29 in. Hg. Same valve class, same numbers — and the letters WOG do not appear anywhere in that three-page document. Apollo has dropped the term entirely in favor of CWP.

Boshart’s knowledge base explains why, and it is worth quoting because it is a manufacturer conceding a point: “The WOG rating has not been a good description and there is movement within the industry to the more descriptive CWP (Cold Working Pressure) rating.” CWP stands for Cold Working Pressure. It says the quiet part out loud — the number is a cold number.

So if you are holding a valve stamped 600 WOG and reading a spec that says 600 CWP, you are not looking at two different products. You are looking at one product and two generations of vocabulary.

Why the steam number is a quarter of the water number

Nothing about the valve changes between 600 and 150. The service does. Saturated steam is hot, and every part in that valve gets weaker as it warms up — the bronze body a little, the seats a great deal.

You can see the seats being the limit in the way the sheets are drawn. Milwaukee’s pressure-temperature chart plots working pressure against working temperature from 0 to 450°F, and it draws two separate curves: one labeled Seat Material Rating and one labeled Saturated Steam. The seat is a plastic. Milwaukee lists it as RPTFE, 15% glass filled. Heat is what it minds.

Milwaukee also adds a footnote against the 600 WOG/150 SWP line that tells you the standard valve is not really a steam valve at all: the company “recommends the use of Stainless steel ball and stem for steam applications.” Apollo makes the same point through its options list, where a 250# steam trim is something you order separately rather than something you get.

Honest limit, and I would rather say it than round it off: neither manufacturer publishes the derating as a table. Both publish it as a graph. That means I can tell you truthfully that the rating falls as temperature rises, and that both sheets draw the curve, but I cannot quote you an exact allowable pressure at 180°F without reading a number off a picture, and I am not going to do that on a page about pressure-bearing parts. If you need the figure for a spec, get it from the manufacturer.

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The G in WOG is not the gas in your gas line

This is the one that matters for safety, and it is the most commonly misread marking in the trade.

People see a valve stamped 600 WOG, read the G as gas, and reach for it to isolate a gas appliance. Boshart’s page is explicit that this is wrong: “WOG does NOT cover combustible gases. Valves for natural gas and liquid propane, for example, must have the required gas approvals from CSA.” The gas in WOG means gases in the compressed-air and inert sense, not fuel gas.

A fuel-gas valve carries its own approval marking, and that marking — not the pressure number — is what makes it legal for the job. Gas work is licensed and permitted work in most jurisdictions in any case. If you are looking at a fuel-gas line, the right move is to confirm the valve’s gas approval and to confirm what your local code has adopted, not to reason from the letters WOG.

The rating that should actually change your purchase: potable water

Here is the finding that made this article worth writing, and it is sitting in plain sight on a mainstream manufacturer’s spec sheet.

Milwaukee Valve’s BA-100 sheet — the same 600 WOG bronze ball valve that turns up in mechanical rooms everywhere — carries an asterisk with this note: “Not intended for use in potable water.”

The valve is perfectly good. It is rated to 600 psi. It is built to MSS SP-110. It simply is not the one to put on your drinking water. The reason lives in the alloy, not the pressure: the body is a cast bronze and the ball and stem are brass, and the lead content of ordinary brass and bronze alloys is exactly what potable-water rules exist to control.

Manufacturers solve this with a parallel product line rather than a footnote. Apollo’s 70-100 data sheet lists its configurations as the standard 70-100 series, a 70LF-100 series — lead-free option, a hose-cap version and a 316 stainless ball-and-stem version. The LF in the middle of that part number is doing more for your house than the 600 on the side of the valve ever will.

So when you are standing in front of a bin of shut-off valves, the pressure marking is the least useful thing stamped on them. Read for the lead-free designation first. If you are choosing the small angle stops and straight stops that feed a sink or toilet, our guide to the best under-sink shut-off valves and angle stops works through which ones hold up and which ones seize, which is the failure that actually happens.

What 600 psi means in a house, which is: nothing

Put the number in context. Most homes run well between 40 and 60 psi, and plumbing code caps household pressure at 80 psi. A valve rated 600 psi cold is therefore carrying roughly ten times the pressure it will ever see.

That margin is real, but it is not a reason to feel clever, because the ways ball valves actually fail in a house have nothing to do with pressure:

• The stem seizes. A valve that never moves for eight years will not move when you need it to. This is the number one failure, and no pressure rating addresses it.
• The seat weeps after a long closure. Plastic seats take a set.
• Somebody left it half open. A ball valve throttled part way wears its seat unevenly.
• The handle rots off outdoors. A steel handle with zinc plating is what Milwaukee lists, and zinc plating is not weatherproofing.

If your main shut-off is a gate valve rather than a ball valve, exercising it is the difference between a controlled repair and a flooded basement — walk the house with our guide to finding and shutting off your water main before you need it in a hurry.

Non-shock is the word doing the most work

Go back to that phrase in the WOG definition: non-shock. It means the rating assumes pressure arrives smoothly. Water hammer is the opposite of smooth — it is a pressure spike that arrives in milliseconds when a fast-closing valve stops a moving column of water.

A ball valve is a quarter-turn valve, which means it is very good at causing exactly that. It is one of the few places where the way you operate a valve matters more than the number stamped on it: close a ball valve slowly on a long run and you avoid the spike entirely. If your pipes already bang, the spike is happening somewhere, and our guide to why pipes bang and how to stop water hammer covers where it comes from and what actually fixes it. Note that high static pressure makes it worse, which is a good reason to know what your house pressure actually is rather than guessing.

How to read a valve you already own

Wipe the body with a rag and turn it to the light. Cast lettering is shallow and takes paint badly, so it is usually legible even on an old valve. You are looking for:

1. A pressure figure with WOG or CWP after it — the cold rating.
2. A second, smaller figure with SWP — the steam rating, if the valve has one.
3. A lead-free mark — often LF in the part number or a separate stamp. This is the one to hunt for on drinking water.
4. A standard, such as MSS SP-110 — both Milwaukee and Apollo list this on their sheets for these valves.
5. A gas approval, if it is on fuel gas. Absence of one is disqualifying.

One caveat on that last pair, stated plainly: MSS SP-110 is a paid standard and I could not open the document itself for this article — the publisher’s site returned a block. So I am telling you what the two manufacturers print on their own sheets, which is that these valves are built to it. I am not telling you what the standard says inside, because I did not read it. Standards are also cited as adopted, and editions move, so confirm what your jurisdiction has adopted before writing a spec.

Frequently asked questions

What does 600 WOG mean on a ball valve?

It means the valve is rated to 600 psi for water, oil or gas, under non-shock conditions and at ambient temperature. WOG stands for Water Oil Gas. It is not a quality grade, and it is not a rating for hot service.

What is the difference between WOG and CWP?

They describe the same rating. CWP stands for Cold Working Pressure, and the industry is moving toward it because it is more descriptive. Apollo’s 70-100 data sheet lists 600 psig CWP and never uses the term WOG at all, while Milwaukee’s BA-100 sheet prints 600 WOG for the same class of valve.

Why is the steam rating so much lower than the WOG rating?

Because steam is hot and the valve gets weaker as it warms. Milwaukee draws two separate curves on its pressure-temperature chart, one for the seat material and one for saturated steam, and its seats are RPTFE. Milwaukee also recommends a stainless steel ball and stem for steam applications rather than the standard trim.

Can I use a 600 WOG valve on a natural gas line?

Not on the strength of that marking. Boshart states that WOG does not cover combustible gases, and that valves for natural gas and liquid propane must have the required gas approvals from CSA. Look for the gas approval, and treat gas work as the licensed, permitted work it is in most jurisdictions.

Is a 600 WOG brass ball valve safe for drinking water?

Not automatically, and this is the marking people should be reading instead. Milwaukee’s BA-100 spec sheet states the valve is not intended for use in potable water. Manufacturers sell a separate lead-free line for that service, such as Apollo’s 70LF-100 series. Look for the lead-free designation rather than the pressure number.

Bottom line

The big number on the side of a brass ball valve is the least decisive thing about it. 600 WOG, or 600 CWP in the newer vocabulary, is a cold, non-shock rating roughly ten times anything a house will produce. 150 SWP is the same valve on steam, and it is lower because heat, not pressure, is the limit. Neither number tells you the thing that should actually pick the valve off the shelf: whether it is rated for drinking water, and whether it carries a gas approval if it is going on gas. Read the letters, not the digits.

Sources

• Milwaukee Valve Company, Inc., BA-100/100S ¼”-3” Bronze Ball Valve specification sheet, BV-1, Rev. 19 — the 600 WOG/150 SWP rating, MSS SP-110, the “Not intended for use in potable water” note, the stainless-trim-for-steam recommendation, the pressure-temperature chart with seat-material and saturated-steam curves, and the materials list.
• Aalberts integrated piping systems, Apollo 70-100 series NPT bronze ball valve data sheet, SS1023, 07/24 — the performance rating box (600 psig CWP, 150 psig SWP, 500°F maximum temperature, 29 in. Hg vacuum service), the MSS SP-110 approval, the 70LF-100 lead-free configuration, and the separately ordered 250# steam trim option. The term WOG does not appear in this document.
• Boshart Industries knowledge base, What does WOG stand for? — the Water Oil Gas expansion, the non-shock and ambient-temperature definitions, and the combustible-gas exclusion.
• Boshart Industries knowledge base, What does CWP stand for? — the Cold Working Pressure expansion and the industry’s movement from WOG to CWP.
• MSS SP-110 is named here only as the two manufacturers list it on their own published sheets. The standard itself is paywalled and was not opened for this article, so nothing is stated about its contents.

Standards are cited as adopted; section numbers and editions move, so confirm what your jurisdiction has adopted before writing a spec.