I manage MRO procurement for a 55-person mechanical services company. Our annual spend on valves, pumps, and shop equipment is around $240,000. In 2024, I audited about 210 purchase orders—maybe 190, I would have to check the system—and found something that changed how I compare parts. The Watts 174A relief valve and the Watts double check valve kept showing up in the same budget line. But they are not interchangeable. That is the first thing to get straight.
According to Watts published product literature (watts.com), the 174A is a relief valve; the Watts double check valve is a backflow preventer. Verify current pressure, temperature, and application ratings before specifying.
How I Am Comparing Them
I am not going to pretend these two valves are A vs. B in the usual sense. The real comparison is: what failure are you preventing? I look at five dimensions: function, installation and hidden labor, maintenance, failure cost, and procurement efficiency. Then I will show how the same logic applies to door hinges installation, upright air compressors, and the question of how long a table saw blade lasts.
Dimension 1: Function — Safety Relief vs. Backflow Prevention
The Watts 174A relief valve is a safety device. Put another way: it is not there to save water or improve pressure; it is there to relieve excess pressure before something else fails. The Watts double check valve is a backflow preventer. It stops contaminated water from moving backward into the supply. If you are comparing them by price alone, you are already off track.
Honestly, I learned this the hard way. In 2023, we had a service tech swap a relief valve for a double check on a boiler-related job because the double check was in stock. It fit. It did not do the job. The callback cost us about $1,200 in labor and overtime. The valve saved maybe $40 upfront. That is not a trade I will make again.
Dimension 2: Installation and Hidden Labor
Installation costs more than the part. For the 174A, you need the right relief setting, discharge piping, and a safe drain path. For a Watts double check valve, you need correct orientation, test ports, and clearance for testing. If you have ever had a valve fail because someone installed it backward, you know that sinking feeling.
This is where the other hardware keywords fit. Door hinges installation looks simple until you are aligning a heavy fire door. A low-cost hinge can mean sagging, rubbing, and repeated adjustments. Fire-rated openings often must meet NFPA 80; verify local code and manufacturer instructions. Same with an upright air compressor: installation includes drain routing, electrical requirements, and clearance for service. A low upfront price can disappear fast in labor.
When I compared our valve callbacks and door-hinge callbacks side by side in Q2 2024, I finally understood why spec matters more than brand logo. Most of our product failures were actually spec failures.
Dimension 3: Maintenance and Lifespan
For the Watts 174A, maintenance is mostly inspection and testing. You check for discharge, corrosion, and proper reseating. For the double check valve, annual testing is often required by local code. Neither is maintenance-free. Never let anyone tell you otherwise.
The upright air compressor follows the same rule. Oil-lubricated units usually need oil changes and filter service; oil-free units avoid oil but may have shorter duty-cycle limits. If you skip the drain, you get rust and water in the lines. That is not a compressor problem; that is a process problem.
How long does a table saw blade last? It depends on what you cut, how you feed it, and whether the saw is aligned. In our shop, a low-cost blade on MDF might last a week. A good carbide blade on softwood can run for months with proper feed rate. I do not trust a single number. I track cuts per blade and cost per cut. That is the only comparison that means anything.
Dimension 4: Failure Cost and Downtime
This is where the comparison gets uncomfortable. A Watts 174A that fails to relieve pressure can cause a safety event. A Watts double check valve that fails can contaminate the water supply. Those are not equal risks. The double check valve is often about compliance and public health. The relief valve is about immediate safety.
The upside of using a lower-cost substitute was saving maybe $38 per valve. The risk was a $1,200 callback or worse. I kept asking myself: is $38 worth potentially a safety incident? The math said no every time.
Same with door hinges installation: a $6 hinge vs. a $14 hinge is not an $8 decision. It is a question of whether the door closes correctly for the next five years. Same with an upright air compressor: a cheaper model with a low duty cycle can cost you production time. Same with saw blades: a blade that lasts half as long but costs 30% less is not a savings if you are changing it twice as often.
Dimension 5: Procurement Efficiency
Efficiency is a competitive advantage. In 2024, we moved our MRO ordering into a shared digital log with photos, model numbers, and failure notes. That simple change cut duplicate orders by about 18%. It also made comparisons faster. When someone asks me Watts 174A vs. Watts double check valve, I can pull up the last 12 months of usage and see the actual application.
Automation does not replace judgment. It just removes the data-entry errors. We still verify every valve against published specs at watts.com. We still test double check valves on schedule. We still check compressor drains. But the efficient process means we catch mismatches before they become callbacks.
For compressed air cleaning, OSHA 1910.242(b) says compressed air shall not be used for cleaning purposes except where reduced to less than 30 p.s.i. and then only with effective chip guarding and personal protective equipment (osha.gov). Verify current requirements.
Which One Should You Buy?
If you are protecting a potable water line from backflow, you need a Watts double check valve—or another approved backflow preventer that meets local code. If you are protecting a system from overpressure, you need a relief valve like the Watts 174A. They are not either/or. They are different jobs.
If you are comparing door hinges installation, choose hinges rated for the door weight, fire rating, and traffic. If you are buying an upright air compressor, match the duty cycle to your actual demand. If you are asking how long a table saw blade lasts, stop looking for a universal number and start tracking cost per cut.
Here is what you need to know: the lowest upfront price is rarely the lowest total cost. I have processed maybe 210 MRO orders—no, 230, I would have to check—and the pattern holds. The expensive option is the one you have to redo.
Quick Procurement Checklist
- Confirm the application: relief vs. backflow prevention.
- Verify published ratings at watts.com before ordering.
- Budget installation labor, not just part price.
- Track failures and cost per cut or cost per cycle.
- For fire doors, check NFPA 80 and local code.
- For compressed air cleaning, follow OSHA limits and verify current rules.