Pipe Caps for Pressure Washing Equipment

Every rig ends up with an open port somewhere. A spare manifold outlet, an unused bypass tap, a tank fitting you are not running this season. A two dollar pipe cap seals it before it leaks or fills with grit. Sun Brite Supply keeps brass caps at the fittings counter in Gaithersburg, MD. Call 301-519-9274 if you are not sure which thread you are looking at.

Cap or Plug? Get the Right One the First Time

People mix these up daily at our counter. A cap is female. It threads over a male fitting, an exposed nipple, or the end of a pipe. A plug is male. It threads into a female port, like an open hole in a pump head or manifold. Look at the thing you want to seal. Threads on the outside means you need a cap. Threads on the inside means you need a plug. Bring the fitting with you if there is any doubt, because NPT sizes are measured by nominal pipe size, not by what you get with a tape measure. A 1/4 inch NPT thread is actually about half an inch across, and that mismatch causes most wrong purchases.

Material is the other call. Our brass cap, at $1.94, handles water, detergents, and heat without rusting, which is why brass is the default on wash rigs. Plated steel works on general plumbing but shows rust once the coating scratches. For daily sodium hypochlorite exposure, step up to stainless fittings instead. Whatever you choose, wrap the male threads with PTFE tape or paste before seating the cap. NPT threads seal on the sealant, not on metal contact alone. And check the pressure rating before capping anything on the high pressure side of the pump. A cap meant for supply lines does not belong on a 4,000 PSI circuit.

Fittings That Go With Caps

• All fittings
• Brass pipe fittings
• Allen head plugs
• Close nipples
• Hex bushings
• Nipple fittings
• Tees and 90 degree elbows
• Or sort it out in person at our Gaithersburg store.

Frequently Asked Questions

What is the difference between a pipe cap and a pipe plug?

A cap has female threads and goes over a male fitting or pipe end. A plug has male threads and goes into a female port. Check whether the threads you need to seal are outside or inside and buy accordingly.

Do I need thread sealant on a cap?

Yes. NPT threads rely on PTFE tape or pipe sealant to make a leak free joint. Two or three wraps of tape on the male threads is enough. Skip it and the cap will weep under pressure.

How do I know what size cap to buy?

NPT sizes run smaller than a ruler suggests, so do not measure the outside diameter and order that number. Match the cap to the fitting's stated NPT size, or bring the fitting to the counter and we will thread it on the spot.

Will a brass cap hold up to chemicals and hot water?

Brass handles hot water and standard wash detergents well. For constant bleach exposure on a soft wash rig, stainless steel lasts longer. Plain plated steel is the first to corrode around chemicals.