Comet Pressure Washer Pumps: Matching PSI, GPM and Fit
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Comet is an Italian pump maker whose triplex plunger pumps show up on many gas and electric pressure washers, and it is a go-to name when an old pump starts leaking or losing pressure. If you searched for “comet pressure washer”, it helps to know that all six products here are really pumps, the part that creates the pressure, rather than complete machines with an engine, hose and wand. Some listings call them pressure washers in the title, but what arrives is the pump head that mounts on your engine or motor.
They differ in three things that decide whether a pump fits: pressure and flow, from a small 2000 PSI, 2.0 GPM unit up to an 8 GPM commercial pump; drive speed, 3400 RPM for direct-drive gas engines versus 1750 RPM for belt or slow motor drives; and shaft size, from 3/4 inch to 1 inch to 24mm.
Comet Pressure Washer Pumps Compared
| Pump | Pressure | Flow | Speed | Shaft |
|---|---|---|---|---|
| Comet ZWD4040G Fully Plumbed | 4000 PSI | 4.0 GPM | 3400 RPM | 1 in hollow |
| Comet BXD2527G | 2700 PSI | 2.4 GPM | 3400 RPM | 3/4 in hollow |
| Comet High Pressure Pump 6305.0914.00 | 4200 PSI | 4 GPM | 3400 RPM | 1 in |
| Comet Pumps 2700 PSI Pump | 2700 PSI | 2.5 GPM | Not listed | Not listed |
| Comet 8 GPM 3500 PSI (PS8010) | 3500 PSI | 8 GPM | 1750 RPM | 24mm |
| Comet AXD2020E | 2000 PSI | 2.0 GPM | Not listed | Not listed |
Here is the jargon in plain English. PSI (pounds per square inch) is how hard the water hits the surface; higher PSI strips tougher grime. GPM (gallons per minute) is how much water flows; higher GPM rinses faster. RPM (revolutions per minute) is how fast the pump expects its input shaft to turn: 3400 RPM matches most gas engines bolted straight to the pump, called direct drive, while 1750 RPM pumps are usually driven by a belt or a slower electric motor. The shaft is the part the engine’s crankshaft slides into, and a hollow shaft pump fits over the engine shaft, so the diameter has to match exactly. A triplex pump uses three plungers for smoother, longer-lasting operation. An unloader redirects water when you release the trigger so pressure does not build up dangerously.
Comet ZWD4040G Fully Plumbed Pump for 4000 PSI Gas Washers
Comet
Comet ZWD4040G Fully Plumbed Pressure Washer Triplex Pump, 4000 PSI, 4.0 GPM, 3400 RPM, 1" Hollow Shaft
Price and specifications are read from the Amazon product page and can change.
Comet ZWD4040G Fully Plumbed Pressure Washer
Best for: Rebuilding a 4000 PSI gas washer
Pros
- 4000 PSI at 4.0 GPM
- Fully plumbed, ready to bolt on
- 1-inch hollow shaft
- Triplex pump design
Cons
- Very sparse listing details
- Heavy at 22.5 pounds
The Comet ZWD4040G Fully Plumbed Pressure Washer Triplex Pump is rated at 4000 PSI and 4.0 GPM at 3400 RPM, with a 1-inch hollow shaft. Fully plumbed means the pump arrives with its fittings and unloader connections in place, so you bolt it to the engine and connect the hoses rather than building the plumbing yourself.
The listing is otherwise very thin. It gives the weight as 22.5 pounds and the finish as brass, but does not describe the unloader, the ports, the plunger material or the recommended engine horsepower. The power source field says “manual”, which is simply a listing error for a pump meant to be engine driven.
This suits someone rebuilding a heavy-duty gas washer whose engine has a 1-inch shaft and turns at 3400 RPM. If you want more detail on the unloader and materials at a similar rating, compare the 6305.0914.00 pump below.
Comet BXD2527G Pump for Homeowner Gas Washers
The BXD2527G Pressure Washer Pump 2700PSI is a smaller pump rated at 2700 PSI and 2.4 GPM, with a maximum speed of 3400 RPM and a 3/4-inch hollow shaft, the size common on homeowner gas engines. The description lists a 5.9 horsepower maximum requirement, which tells you the engine size it expects.
It has one of the most detailed descriptions here: built-in easy start, a double sealing system, stainless steel plungers and check valves, a steel shaft with built-in key, an oil level sight glass so you can see oil without opening it, a forged brass manifold, a ball bearing design, a 1/2-inch FPT inlet and a 3/8-inch male NPT outlet. It weighs 11 pounds. The brand name field shows a different company name from Comet, although the manufacturer is listed as Comet Pump, so the listing is inconsistent.
Pick this if your current washer has a 3/4-inch shaft engine of around 5 to 6 horsepower and you want a direct replacement. The listing does not say whether an unloader is included, so check before ordering.
Comet High Pressure Pump 6305.0914.00 for Heavy-Duty Rigs
American Pressure
Comet High Pressure Pumps (6305.0914.00)
Price and specifications are read from the Amazon product page and can change.
Comet High Pressure Pumps
Best for: Heavy-duty 4 GPM gas rigs
Pros
- 4200 PSI at 4 GPM
- VRT-3 unloader with easy start
- Ceramic plungers
- Thermal relief valve
Cons
- Needs 1-inch shaft engine
- Part number is only name
The Comet High Pressure Pumps listing, part number 6305.0914.00, is a fully plumbed direct-drive triplex plunger pump rated to 4200 PSI at 4 GPM, 3400 RPM, with a 1-inch shaft. It includes a VRT-3 multi-function unloader with easy start, which reduces back pressure so the engine starts without load, plus a thermal relief safety valve and an inline fuel filter.
Build details include forged bronze connecting rods (described with a lifetime warranty), hardened stainless steel piston guides, stainless steel check valves, ceramic plungers that resist abrasion and heat, double-sealing V-packings and a die-cast anodized aluminum crankcase with fins for cooling. It weighs 14.5 pounds.
This is the pump for someone who wants the highest pressure in this group on a 1-inch shaft engine and values a clearly described unloader. It is the more fully documented alternative to the ZWD4040G. If you would rather buy a complete ready-to-use machine, our guide to electric power washers is a simpler starting point.
Comet Pumps 2700 PSI 2.5 GPM Pump for Known Replacements
The Comet Pumps Pressure Washer Pump is rated at 2700 PSI and 2.5 GPM according to its title, and that is essentially all the listing says. It does not specify the model number, shaft size, RPM, ports, weight or whether an unloader is included.
Without those details, it is impossible to confirm fit from the listing alone. Its pressure and flow are close to the BXD2527G, but the slightly higher flow suggests it is a different model.
Buy this only if you already know the exact part your machine needs and can confirm it with the seller. For a first-time rebuilder, the BXD2527G’s full specs make it the safer choice.
Comet 8 GPM 3500 PSI Pump PS8010 for Commercial Cleaning
Comet
8 GPM 3500 PSI 1750 RPM 24mm Shaft Pressure Washer by COMET
Price and specifications are read from the Amazon product page and can change.
8 GPM 3500 PSI 1750 RPM
Best for: Commercial high-flow cleaning setups
Pros
- 8 GPM at 3500 PSI
- Ceramic plungers, bronze rods
- Tapered roller bearings
- No oil leak crankcase system
Cons
- Needs 1750 RPM drive setup
- 24mm shaft limits engine fit
The 8 GPM 3500 PSI 1750 RPM 24mm Shaft pump by Comet, model PS8010, is a different class: a high-flow pump for commercial cleaning. At 8 GPM it moves twice as much water as the 4 GPM pumps, which rinses large areas like fleet trucks or parking lots faster. It runs at 1750 RPM with a 24mm solid shaft, so it is designed for belt drive or a matched motor, not a standard 3400 RPM direct-drive gas engine.
Listed features include a forged brass head and manifold, die-cast aluminum alloy for corrosion protection, heat-treated stainless piston guides, stainless check valves, solid ceramic plungers, solid bronze alloy connecting rods, tapered roller bearings, a large oil capacity, long-life seals and a patented no-oil-leak crankcase system. The description also mentions a TW8036 PS8010S designation, and it does not say whether an unloader is included.
This is for professionals building or rebuilding a commercial rig. It is not a drop-in for a homeowner washer.
Comet AXD2020E Pump for Small Electric Washers
The 2000 PSI 2.0 GPM Pressure Washer listing by Comet, model AXD2020E, is a small pump rated at 2000 PSI and 2.0 GPM, and it comes with an unloader and injector. An injector draws detergent into the water stream, so you can apply soap through the same hose. Comet says it is made ready to install and can be used immediately as a replacement for an old pump.
The listing does not specify shaft size, RPM, weight or mounting pattern, so you will need to compare your old pump’s model number carefully.
This suits a light-duty washer for cars, patios and decks. If you prefer a cordless or plug-in machine instead of rebuilding, see our battery power washer guide.
How to Choose the Right Comet Pump
Match the shaft first. A pump will not mount if the shaft does not match: 3/4 inch for the BXD2527G, 1 inch for the ZWD4040G and 6305.0914.00, 24mm for the PS8010.
Match the RPM. Direct-drive gas engines usually turn 3400 RPM. The 1750 RPM PS8010 needs a belt or slower motor.
Match PSI and GPM to your engine. Higher numbers need more horsepower. The BXD2527G lists 5.9 horsepower; larger pumps need larger engines.
Check what is included. Fully plumbed pumps and the AXD2020E include an unloader. Others may not.
FAQ
Are these complete pressure washers?
No. Despite some titles, they are pumps that mount to an engine or motor you already own.
What does fully plumbed mean?
The pump comes with fittings and unloader connections installed, ready to connect.
Can I put a 1-inch shaft pump on a 3/4-inch engine?
No. The hollow shaft must match the engine shaft size.
Which Comet pump gives the most pressure?
The 6305.0914.00 is rated to 4200 PSI at 4 GPM.
What is the difference between 3400 and 1750 RPM pumps?
3400 RPM pumps bolt straight to typical gas engines. 1750 RPM pumps usually run from a belt or matched motor.
