Comet Pump Parts

Comet pump parts are cheap insurance next to the cost of a new pump. We stock seal kits, piston kits, valve parts, oil, and hardware for the AXD, LW, ZWD, FW, RW, SW, and TW series at our Gaithersburg counter. Read the model plate on your pump and call 301-519-9274. We will pull the right kit while you are still on the phone.

How to Find the Right Comet Pump Repair Parts

Every Comet kit is series and size specific, so the job starts at the model plate riveted to the pump crankcase. The letters tell you the series and the numbers point to flow and pressure. A ZWD 4040 is a ZWD series pump rated 4 GPM at 4,000 PSI. Order parts by the series and the plunger diameter, not by what the machine brand calls itself. Plenty of big-box machines hide a Comet AXD under the shroud, and the machine brand's parts diagram will cost you twice what the Comet part number does.

Plunger diameter is the spec people miss. Comet builds the same series with 14mm, 15mm, 18mm, and 20mm plungers depending on the flow rating, and an 18mm seal kit will not seal a 15mm plunger. If the plate is gone, pull a head bolt and measure the plunger with calipers. Or bring the pump in and we will measure it for you.

Match the Symptom to the Kit

Do not guess. Each failure has a signature, and the signature tells you which kit to buy.

Stock levels move daily, so call ahead if the job is waiting on the part.

Cold Water Kits vs Hot Water Kits

Comet sells two seal materials for a reason. Standard seals live a full life on cold water machines and die young at 200 degrees. The hot water kits use high-temp material that shrugs off coil heat. They cost more, and on a hot machine they are worth every dime. If your hot water rig eats a standard seal kit in a season, you bought the wrong kit, not a bad pump. One more habit that doubles seal life on any machine: never let the pump sit in bypass. Trapped water heats up fast and cooks seals from the inside, even on a cold water unit.

Rebuild Tips From the Bench

A Comet seal swap is a bench job, not a machine shop job. You need hand tools, a vise, and about an hour the first time. Three things trip people up. First, keep the valve parts in order when you pull the caps, because mixing seats and poppets between cylinders causes pulsing. Second, lubricate new seals with clean pump oil before pressing them in, since dry seals tear on installation more often than they fail in service. Third, torque the head bolts evenly in a cross pattern. Cranking one corner down first warps the manifold and you get a leak that looks exactly like the one you just fixed.

From the Field

Look at what sells in this collection and the story writes itself. Seal kits outsell piston kits about three to one, and most of the piston kits go out the door in winter and early spring. That is freeze damage. Water left in the head over a cold night expands and cracks ceramic plungers, and a $10 quart of pump antifreeze would have saved a $200 kit. The other pattern is oil. We sell dip sticks, sight glasses, and Comet pump oil to the people who make their pumps last. Change the oil at 50 hours, watch the sight glass for milkiness, and your crank end will outlive two sets of seals.

Related Collections

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• Pump oils and crankcase supplies
• Packing extraction tools for stubborn seals
• Unloader valves, the other half of most pressure complaints
• General Pump parts, CAT pump parts, and AR pump parts
• All pressure washer repair parts
• Near Gaithersburg? Our parts counter can measure your plunger and match kits same day

Frequently Asked Questions

How do I identify my Comet pump model?

Find the metal plate on the pump crankcase. The letter code is the series, like AXD, LW, ZWD, or FW2, and the numbers give flow and pressure. Order parts by that code, not by the pressure washer brand on the frame.

Do I need a seal kit or a piston kit for my Comet pump?

Pressure loss with water weeping below the head points to water seals. If you open it up and the ceramic plungers are scored or chipped, add a piston kit. Inspect before you order, since running new seals over damaged plungers destroys the seals in hours.

What size seal kit does my Comet pump take?

Comet uses 14mm, 15mm, 18mm, and 20mm plungers across its series. The model plate or the parts breakdown for your exact model tells you which. When in doubt, measure the plunger or call us with the full model number.

Why did my hot water machine eat its pump seals so fast?

Standard seals are not built for coil temperatures. Use the hot water version of the kit on any burner-equipped machine. Long bypass time makes it worse, so do not let the machine idle with the gun closed.

Is rebuilding a Comet pump hard?

No. With hand tools and an hour you can do a seal kit on the machine's frame. Keep valve parts in order, oil the new seals before installing, and torque the head evenly. First-timers get it right far more often than they expect.

Why is the oil in my Comet pump milky?

Water is getting past the low-pressure seals into the crankcase. Change the oil now, run it briefly, and check again. If it turns milky again, install new seals before the crank bearings pay the price.

Can you cross-reference my machine brand to a Comet part number?

Usually, yes. Many machine brands rebadge Comet pumps. Call 301-519-9274 with the pump plate info or text us a photo and we will match the kit.