Stainless pump heads cost more than brass, and most of the time you do not need one. The cases where you do are specific, and they have less to do with pressure or temperature than with chemistry.

What actually attacks a brass head

Brass holds up fine against plain water and most general-purpose detergents. It fails against three things in particular.

• Chlorides. Bleach, sanitizers, and salt water. Chlorides attack brass through dezincification, where the zinc leaches out and leaves a porous copper structure behind. The part keeps its shape and loses its strength, which is why the failure is often sudden.
• Caustics. High-pH cleaners, the kind used for grease and protein in food plants.
• Quaternary ammonium compounds. Common sanitizers, and rough on brass over time.

If any of that goes through your pump regularly, a stainless head pays for itself. If you are running water and ordinary soap, it will not.

Stainless is not one material

The grade matters and the catalog tells you which one.

316L contains molybdenum, which is what gives it real chloride resistance. This is the grade you want for bleach, sanitizers, salt water and marine work. The XWLSS50.20NB at 13.2 GPM and 3,000 PSI is a 316L head.

420 is a hardenable martensitic stainless, used where food-contact approval and strength matter more than maximum chloride resistance. The RTDSS80-300N at 21 GPM and 4,350 PSI has a food-grade 420 head.

If someone sells you “stainless” without saying which grade, ask.

The thing people get wrong

A stainless head does not make a pump hot-water rated. Those are two separate specifications and they are set by two different parts.

The head material determines chemical compatibility. The seal material determines temperature limits. You can buy a stainless-head pump with seals that will not survive hot water, and you can buy a brass-head hot-water pump. Check both.

The seal options show up in the part number and in the description:

The HW in a part number is the hot water indicator, not the SS. RHWASS6G30N at 6 GPM and 3,000 PSI is both: stainless head and PTFE seals.

Stainless pump heads by size

Why the same part number appears at two pressures

Worth understanding, because in the RKA-SS family it looks like an error and is not.

AR rerated the solid shaft stainless pumps to 3,000 PSI without renaming them. The flange versions were not rerated and genuinely remain at 1,500. So RKASS4.2G15N is 4.2 GPM at 3,000 PSI, while RKASS42G15E-F33 is 4.2 GPM at 1,500, and both are current. The G15 in the name tells you nothing about which.

The general rule across AR’s catalog: flow and the shaft and flange suffixes decode reliably, pressure does not. Read the pressure off the listing for the exact model before you size a motor around it.

At the extreme end, the STPA-SS55G70N runs 5.5 GPM at 7,000 PSI with a stainless head.

Do not mix metals

If you spend the money on a stainless head and then thread brass quick-connects into it, you have built a galvanic couple. The brass becomes the anode and corrodes faster than it would have on its own. Match the fittings to the head, all the way to the gun.

This is the most common way a stainless upgrade gets wasted, and it is entirely avoidable.

Keeping a stainless pump head working

• Flush with clean water after every chemical run. Stainless resists corrosion; it does not enjoy sitting in bleach overnight.
• Check the seal drain area for weeping, since that is your early warning on the seal set.
• Follow the oil interval. The head material has no bearing on the crankcase.
• Winterize it. Stainless does not stop water from expanding when it freezes.

Browse the full stainless steel pump range. If you tell us what chemistry you are running and at what temperature, we can tell you which head and which seals you need. Contact us here.