Comet Pressure Washer Pumps

Comet has been building plunger pumps in Italy since 1959, and contractors keep choosing them for a simple reason: rebuild parts are affordable and easy to get. Sun Brite Supply stocks Comet pressure washer pumps from the entry AXD axial series up to the big TW belt-drive triplex models, along with the seal and piston kits that keep them earning. Call 301-519-9274 with your engine model and GPM target and we will match the right pump on the first try.

Which Comet Pump Series Do You Need?

Comet builds two very different kinds of pumps, and the price tags reflect it. The AXD, BXD, and AWD series are axial pumps. A wobble plate drives the pistons, the hollow shaft slips straight over a 3/4" or 1" engine shaft, and the whole unit stays compact and cheap. They are the right call for homeowner machines and light-duty rigs that run a few hours a week.

The ZWD, LW, FW, RW, and TW series are triplex plunger pumps. Three ceramic plungers run in a brass manifold, driven by a crankshaft like a small engine. They cost more, but they rebuild over and over and shrug off daily commercial hours. The ZWD is the direct-drive contractor workhorse. LW models cover compact electric and small gas machines. FW and FWS2 pumps step up to 18mm plungers at 1,450 to 1,750 RPM. RW and TW models are 24mm solid-shaft pumps built for belt-drive rigs, with the TW reaching 8.7 GPM and 5,000 PSI ratings.

How to Read a Comet Model Number

The model number tells you almost everything. Take ZWD4040G: the first pair of digits is flow times ten, so 40 means 4.0 GPM. The second pair is pressure divided by 100, so 40 means 4,000 PSI. The letter on the end is the drive: G is a gas engine flange, E is an electric motor flange, S is a solid shaft for belt or pulley drive. A K suffix means the pump ships as a kit with the unloader already plumbed. Once you can read that code, comparing pumps takes seconds.

Comet Pump Quick Reference

Prices move with the market. The popular ZWD gas-flange models sit on our Gaithersburg shelf most of the year, and one phone call confirms current stock on anything else.

Keeping a Comet Pump Alive

Comet's own service schedule is stricter than most owners realize. Check the oil level on the dipstick every 8 running hours. Clean the inlet filter every 50 hours, because a starved pump cavitates and eats its own valves. Change the oil at the first 50 hours to flush break-in metal, then every 500 hours after that, using Comet pump oil rather than motor oil. Have the suction and delivery valves looked at around the 500 hour mark too.

Two more numbers matter. Cold-water Comet pumps are rated for water up to about 140 degrees F, so do not feed them off a hot water heater unless the pump carries hot-water seals. And if your rig sleeps outside in a Maryland winter, push antifreeze through the head or the first freeze will crack the manifold. That repair usually costs more than the pump is worth.

From the Field

Look at what sells across this counter and the pattern is obvious. We move far more Comet seal kits and piston kits than complete pumps, because a tired ZWD or FW almost always comes back with a $75 to $215 rebuild instead of a $550 replacement. Water dripping from the weep holes under the manifold means the low-pressure seals are going. Milky oil means water has crossed into the crankcase and the oil seals are next. Pressure that surges and drops usually traces to a sucked-flat inlet hose, a clogged filter, or a fouled check valve before it is ever the pump's fault. Bring us the model number off the pump tag and we will pull the exact kit from our Comet pump parts wall.

Related Collections

• Comet pump parts and rebuild kits
• All pressure washer pumps
• Pumps Made Ready assemblies
• Unloader valves
• Pump oil
• AR pumps
• General Pump models
• Udor pumps
• CAT pumps

Local crews can skip shipping and pick up the same day at our Gaithersburg pressure washer store.

Frequently Asked Questions

What do the numbers in a Comet pump model mean?

The first two digits are flow times ten and the next two are pressure divided by 100. A ZWD4040G flows 4.0 GPM at 4,000 PSI. The final letter is the drive: G for gas flange, E for electric flange, S for solid shaft.

Is a Comet AXD pump good enough for commercial work?

Not really. The AXD is an axial wobble pump built for homeowner and light-duty hours. If you wash for a living, step up to a ZWD triplex or a belt-drive RW or TW. The rebuild economics alone justify it.

What oil goes in a Comet pump and how often do I change it?

Use Comet pump crankcase oil, never motor oil. Change it after the first 50 hours of break-in, then every 500 hours or once a season. Check the dipstick level every 8 running hours.

Why is my Comet pump pulsing or dropping pressure?

Check the cheap stuff first: a clogged inlet filter, a kinked or collapsed supply hose, air leaking into the suction side, or a worn nozzle. If those pass, worn packings or a fouled check valve are next, and a seal kit fixes both.

Will a Comet ZWD pump fit my Honda GX390?

Yes. The 1" gas flange ZWD models bolt directly to a GX340 or GX390 shaft. Smaller GX160 and GX200 engines take the 3/4" flange versions. Match pump horsepower demand to the engine and you are set.

Can I rebuild my Comet pump instead of replacing it?

Almost always. Seal kits, piston kits, and valve kits are available for the AXD, ZW, LW, FW, RW, and TW series, and most swaps take under an hour with hand tools. We stock the common 15mm and 18mm kits.