Choosing between a centrifugal chemical process pump and an air-operated double diaphragm pump usually comes down to how your flow control system runs. Do you need a permanent high-pressure pump connected to process piping, or do you need a more flexible pump that can handle different fluids and lower flow rates without a big capital outlay? Here's how the Durco Flowserve MK3 and the 120PSI air-operated diaphragm pump stack up for real shopping decisions.
Quick Verdict
If your operation calls for continuous chemical transfer at higher pressures, the Durco Flowserve MK3 is the serious process pump. If you're looking for a low-cost air-driven diaphragm pump for 35 GPM or less and can work with 120 PSI, the $126.01 model is a completely different economic proposition. The $3,750 Flowserve costs $3,623.99 more than the diaphragm pump, and that price gap reflects differences in pump type, pressure rating, and intended duty.
At a Glance
| Product | Listed Price | Pump Type | Pressure | Connections |
|---|---|---|---|---|
| Durco Flowserve MK3 | $3,750.00 | Centrifugal chemical process pump | 275 PSI @ 100°F | 1.5" x 1" |
| 120PSI Air-Operated Double Diaphragm Pump | $126.01 | Air-operated double diaphragm pump | 120 PSI | 1" inlet/outlet, 1/2" NPT air inlet |
Where Each Product Wins
Durco Flowserve MK3 wins for higher pressure process duty. It's a 1.5-inch by 1-inch centrifugal pump from the MK3 STD series with a 275 PSI rating at 100°F, which makes it a candidate for permanent chemical process lines.
120PSI Air-Operated Double Diaphragm Pump wins for upfront cost and air-driven operation. At $126.01, it costs $3,623.99 less than the Flowserve, and its positive displacement design handles 35 GPM at 120 PSI with a 1-inch inlet and outlet.
Product Notes
Durco Flowserve MK3 Chemical Process Centrifugal Pump
The Durco Flowserve MK3 is a 1.5-inch by 1-inch centrifugal chemical process pump with a Model MK3 STD designation and a D4 material spec. It's listed as new open-box surplus, and it's rated for 275 PSI at 100°F, which puts it in a different pressure class than the diaphragm pump. This is the pump to choose when you're setting up a permanent process line and need continuous, higher-pressure transfer through 1.5-inch and 1-inch piping. The Flowserve name and MK3 series signal a purpose-built chemical process pump. The trade-off is the $3,750 listed price and the open-box surplus condition, so you're making a larger upfront commitment for a unit that isn't sold as a standard retail item. If your system only needs 120 PSI and 35 GPM, this is more capacity and cost than the job requires.
120PSI Industrial Chemical Air-Operated Double Diaphragm Pump
The 120PSI Industrial Chemical Air-Operated Double Diaphragm Pump is a positive displacement pump with 1-inch inlet and outlet ports, an aluminum body, a nitrile diaphragm, and acetal balls. It's rated for up to 35 gallons per minute at 120 PSI and handles temperatures up to 150°F. The 1/2-inch NPT air inlet and 38 CFM average air consumption mean you need a steady compressed-air supply, but the pump's $126.01 price makes it an easy entry point for moving petroleum fluids and other compatible liquids. The main limitation is the lower pressure ceiling: at 120 PSI, it can't replace a 275 PSI process pump. You'll also want to make sure your fluid is compatible with nitrile and acetal wetted materials. For smaller transfer jobs that fit within those specifications, the cost and simplicity are hard to beat.
Final Choice by Use Case
Choose the Durco Flowserve MK3 if you're investing in a permanent chemical process line that needs higher pressure and continuous centrifugal flow. Its 275 PSI rating and 1.5-inch by 1-inch process connections make it the industrial-grade option, but the $3,750 price means the decision should be part of a real capital budget.
Choose the 120PSI Air-Operated Double Diaphragm Pump if you're moving compatible fluids at 35 GPM or less, need positive displacement pumping, and want to stay around $126. It won't hit the Flowserve's pressure levels, but for the right application it gets the job done without the high price tag.
