The BIG “O” (ring) and Many $$

Folks, there’s a lot you need to know about marketing, markup, and money when it comes to maintaining numerous household products found in the typical modern home and yard. Primarily, it’s all about saving money, your money!

If you have a pool or spa, this will be of particular interest to you, but can apply to maintenance of many other household devices and systems. This will give you some insight into a system designed to pry money out of your wallet that you just don’t need to spend.

The other morning, I walked out to the pool and noticed a small puddle forming under the pump. Closer inspection indicated that the pump volute O-ring was beginning to seep under pressure. But, since in the many years I have been maintaining this pool equipment, this wasn’t the first time, I knew that a simple cleaning of all the mating surfaces combined with a nice new flexible and well lubricated O-ring would fix it right up.

Since it was a very small leak, this time I decided to try and find the new O-ring online, hoping to save a few bucks over the local pool store price. Using the part number, 39006000, I did a quick search and found numerous offers for this particular O-ring ranging in price from around $6.00 plus shipping to as much a $13.25.

Pump Flange
Pump Volute O-Ring

Usually, when I have to replace this O-ring, I typically do a more thorough job, and use the opportunity to replace the O-ring on the leaf filter basket lid also, cleaning and lubricating the locking cams and lock ring too.

This leaf filter basket lid O-ring, part number 39300600, is also available from various pool supply outlets for prices as high as $32.99 with free shipping, although typically more like $10 + shipping.

Lastly, I also frequently need the O-ring for the top of the in-floor cleaning heads switching valve, and the square cut rings that go on the bottom of the heads themselves. These are also available locally, with the distributor valve O-ring costing $18.99 and the cleaning head rings costing $10.99 at the pool store.

So, to do this maintenance and maybe keep a few spares in stock, I’m looking at an average of around $12 per O-ring, with the distributor valve slightly higher at around $15.

Pump Volute O-ring                        $12

Filter Basket Lid O-ring                 $12

Switching Valve O-ring                  $15

Cleaning head rings (15)                $165

Shipping                                            $ 8

TOTAL   ——————->            $212


NO WAY! $212 just for a few rubber rings? NO WAY!

Luckily, I’m aware that millions of industrial products rely on O-rings to perform their functions without leaking, and that O-rings generally come in standard sizes. Additionally, most “household” O-rings are made of a material called “Buna-N” otherwise known as Nitrile in one of two hardness (or softness) grades, that define their “squishability,” 70 or 90 durometer hardness, with 70 being the more common.

Now were are not talking about space shuttle fuel tank O-rings here, we are talking about pool parts. So any generic Buna-N O-ring of the right size will work.

A long time ago, the Society of Automotive Engineers decided that common O-rings should conform to a specified standard. So, they conceived and published a chart of standard sizes and called it Aerospace Standard 568 or AS568. (OOPS, we’re back to space shuttle O-rings, but sizing isn’t rocket science!)

If you look up any AS568 sizing chart (use Google), you will see that all common O-rings fall into 5 groups, divided by the thickness of the actual ring itself.

Group “0” = 1/16”

Group “1” = 3/32”

Group “2” = 1/8”

Group “3” = 3/16”

Group “4” = 1/4”

Then, within each group, a number of progressive sizes are available and are numbered consecutively. The first digit identifies the group or thickness of the cross section, and the second and third digits the consecutive place in the order, hence the diameter of the O-ring itself.

So, looking at a chart, we see that an AS568 – 329 is in group “3” indicating an O-ring that is 3/16” thick and number “29“ size which has an inside diameter of 2”. Logically, it has an outside diameter of 2 3/8” which is the inside diameter of 2” plus the added thickness of the O-ring times 2. Keep in mind that these are “nominal” specifications, and that most charts will give the exact dimensions in decimal inches with a tolerance value, but for our use, nominal is plenty good enough.

AS568-329 O-ring

So, to save a whole bunch of money, I carefully measured the existing O-rings and the dimensions of the parts that they are designed to seal on my pool equipment, and determined that the following standard AS568 sizes apply to my American Products Ultra-Flow Pump and AA Manufacturing 5 port distributor valve.


Pump Volute O-ring                        AS568 -449         ( 10″ID X 10-1/2″OD X 1/4″CS )

Filter Basket Lid O-ring                   AS568 -439           ( 6-1/2″ID X 7″OD X 1/4″CS )

Switching Valve O-ring                   AS568 -267          ( 8-1/4″ID X 8-1/2″OD X 1/8″CS )

Cleaning head rings                       -139 Square Cut   ( 2 3/16″ID X 2 3/8″OD X 3/32″CS )


Now, a good online source like, makes it easy to order these O-rings generically, rather than paying pool store prices. All the ones I am specifying are “70” durometer Buna-N black rubber O-rings, the most common.

Pump Volute O-ring                        AS568 -449         B70449           $1.78

Filter Basket Lid O-ring                   AS568 -439         B70439          $1.07

Switching Valve O-ring                   AS568 -267         B70267           $0.50

Cleaning head rings (5)                  -139 Square Cut SN70139         $0.32 (min qty. 15 = $4.80)

Shipping                                                                                                    $7.00

TOTAL   ————————————————————— >        $15.15    

That’s right, pool store prices are approximately $212.00!   I ordered them for $15.15.

Lastly, some applications may be better off with a softer, “squishier” O-ring made of silicone instead of Buna-N. Silicone O-rings aren’t very good where the two pieces that require their seal undergo sliding or rotary relative motion, but for all my applications, the seal is just compressed in place and stays there. So, for the switching valve and the filter basket lid, silicone works even better than Buna-N and can be disassembled and reassembled repeatedly without leaks. So in the long run, silicone can save money by being re-used rather than replaced each time, even though it costs more initially. Here are the same O-rings in 70 durometer silicone.

The square cut rings are not available in silicone.

Pump Volute O-ring                        AS568 -449         S70449           $3.18

Filter Basket Lid O-ring                  AS568 -439         S70439           $1.95

Switching Valve O-ring                   AS568 -267         S70267           $1.20

Cleaning head rings (5)                  -139 Square Cut SN70139       $0.32 (min qty. 15 = $4.80)

Shipping                                                                                                 $7.00

TOTAL   ————————————————————— >        $18.13    


Ultimately, with a little careful measuring, some hunting on the internet, and a willingness to wait for the mailman, I saved just under TWO HUNDRED DOLLARS!

You decide what you’ll do when you need a new O-ring the next time you are doing a little maintenance.

Finally, I have been asked about the Harbor Freight O-ring assortment boxes that give you nearly 400 assorted O-rings for around $8. For the most part, they are sufficient, and I have used many out of the kits I have bought. They offer “Nitrile” (Buna-N) kits in numerous size combinations in SAE or Metric. As always, do not use generic O-rings in specialty applications, such as automotive air conditioning or braking systems, and never attempt to fix gas appliances yourself. The risk is just too great.

Sizes in these kits are logically limited, but unless you need a really large or odd size, they will satisfy most applications. In my case, since there are no square cut rings in the box, and the largest is 1 ¾” I.D., I had to order them online individually.