Petersen 18958AW
1/2 in · Hose barb
Half-inch barb with evacuation flange. Compare the original valve before ordering.
Petersen RV Fresh-Water Drain Valves: Barb vs Threaded Guide
A slow leak at the fresh-water tank drain may be caused by a worn valve, but not every plastic low-point drain has the same plumbing connection. Petersen Molding offers both hose-barb and male-threaded styles in 3/8-inch and 1/2-inch sizes. Use this guide to distinguish the physical connection and match the exact part number on your original assembly before buying a replacement.
Check the fitting style before choosing a drain valve
Hose-barb connectionA barbed end inserts into appropriately sized flexible tubing, normally secured according to the tubing manufacturer's requirements. Measure the tubing and identify the original barb size.
Male-threaded connectionA threaded end fits a matching female port with the correct thread type and sealing method. A 3/8-inch threaded end is not a substitute for a 3/8-inch hose barb.
Mounting and outlet detailsCompare the valve body, lever movement, evacuation flange and clearance around the tank. Two valves with the same inlet size may have different mounting or handle configurations.
Fitment check: These are fresh-water tank drain valves, not black- or grey-water sewer gate valves. A matching nominal 3/8-inch or 1/2-inch size does not prove interchangeability: confirm the original valve's connection, mounting and full MPN.
Petersen fresh-water drain valve comparison by part number
These catalogue-listed sizes distinguish hose-barb and threaded versions. The AW and CW suffixes are retained as separate product numbers; do not assume they are interchangeable merely because their connection styles appear the same.
| Petersen MPN | Connection size | End style | Additional identification | Part |
|---|---|---|---|---|
| 18957CW | 3/8 in | Male threaded | Threaded male end; listed with evacuation flange | View |
| 18958AW | 1/2 in | Hose barb | Half-inch barb with evacuation flange | View |
| 18958CW | 1/2 in | Hose barb | Half-inch barb with evacuation flange; distinct MPN | View |
| 18959AW | 3/8 in | Hose barb | Three-eighths-inch barb with evacuation flange | View |
| 18959CW | 3/8 in | Hose barb | Three-eighths-inch barb with evacuation flange; distinct MPN | View |
| 18964BLACK | 3/8 in | Male threaded | Black drain valve with male threaded connection | View |
| 18966AW | 1/2 in | Male threaded | Half-inch male threaded drain valve | View |
| 18966CW | 1/2 in | Male threaded | Half-inch male threaded drain valve; distinct MPN | View |
Compare Petersen drain valves with product photos
Each card links to the exact listing in our store. Where the original valve is unmarked, use its plumbing end and body configuration to narrow the candidates and compare the product photograph against the removed part.
Hose-barb drain valves
Petersen 18958CW
1/2 in · Hose barb
Half-inch barb with evacuation flange; distinct MPN. Compare the original valve before ordering.
Petersen 18959AW
3/8 in · Hose barb
Three-eighths-inch barb with evacuation flange. Compare the original valve before ordering.
Petersen 18959CW
3/8 in · Hose barb
Three-eighths-inch barb with evacuation flange; distinct MPN. Compare the original valve before ordering.
Male-threaded drain valves
Petersen 18957CW
3/8 in · Male threaded
Threaded male end; listed with evacuation flange. Compare the original valve before ordering.
Petersen 18964BLACK
3/8 in · Male threaded
Black drain valve with male threaded connection. Compare the original valve before ordering.
Petersen 18966AW
1/2 in · Male threaded
Half-inch male threaded drain valve. Compare the original valve before ordering.
Petersen 18966CW
1/2 in · Male threaded
Half-inch male threaded drain valve; distinct MPN. Compare the original valve before ordering.
Questions about choosing a fresh-water drain valve
Can I replace a barbed valve with a threaded Petersen valve?
Not as a direct replacement unless the plumbing was designed for that connection. Threaded ports and hose barbs require different matching fittings. Verify the installed tank outlet and the plumbing arrangement.
Are 18958AW and 18958CW the same product?
Both are listed with a 1/2-inch hose-barb end, but they carry separate part numbers. Check the original valve's complete MPN, body shape and colour rather than assuming equivalence.
Which models have an evacuation flange?
The current listings identify evacuation flanges on 18957CW, 18958AW, 18958CW, 18959AW and 18959CW. The other listed versions should be compared individually to the original before making assumptions about flange construction.
Does a Petersen freshwater valve replace a holding-tank sewer valve?
No. These small valves are intended for fresh-water tank draining. A sewer holding tank typically uses an entirely different waste valve assembly and connection system.
More freshwater system references
To identify surrounding plumbing parts, see our RV water pump, city-water inlet and strainer reference and RV city-water fitting identification guide. For winterizing, follow the RV winterizing parts guide.
Identify the original valve and tank connection before draining or disassembling the fresh-water plumbing.
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