RCP-C15123D4: two compressors on one tank, so a service visit does not stop the shop

A duplex compressor is not a bigger compressor. It is two complete compressors — two cast iron pumps, two motors, two sets of controls — sharing a single 120 gallon ASME receiver, with an alternator deciding which side runs. That architecture answers a question single-machine buyers only ask themselves once, usually on the morning the compressor fails: what happens to the shop when there is no air?

With this machine the answer is that the shop keeps working. You can isolate one side for maintenance, a belt change, a pressure switch or a full pump rebuild, and still have air from the other. In a business where every bay depends on the compressor, that is the difference between a scheduled inconvenience and a day of lost labour.

How the alternator earns its place

The included alternator swaps which pump starts first. Without it, one pump would take every start and every hour while the second sat as a cold spare, aged badly and then failed the first time it was genuinely needed. Alternating shares the wear, keeps both halves exercised, and means that when you do isolate a side, the one still running is a machine with a known service history rather than an unknown quantity. On heavy demand both sides can contribute; on light demand one side handles it alone. Magnetic starters are included with the package.

Cast iron, two stage — and why that combination is still specified

The pumps are solid cast iron and two stage. Two stage means the air is compressed twice with cooling in between, which is how the machine reaches a 175 psi maximum without the discharge temperature that a single-stage pump would produce chasing the same pressure. It rates 46 CFM at 100 psi.

Cast iron is the other half of that. It is heavy, it conducts heat away from the cylinder, and it is rebuildable — rings, valves and gaskets are serviceable items rather than a reason to scrap the pump. That is why cast iron two-stage compressors remain the specification in shops that intend to own equipment for a very long time, and it is a large part of why this unit weighs about 1,131 lbs. The weight is a feature, not a shipping problem, though you will have to treat it as both.

A pressure figure on this listing we want to flag

One number on this page does not agree with the others, and we would rather point at it than hope you do not notice.

• The feature list describes the machine as 2 x 7.5 HP duplex — two motors of 7.5 HP each.
• The product title is consistent with that, describing the unit as 15 HP in total.
• A horsepower summary field on the listing, however, reads 8 HP, which matches neither the pair nor the total.

Two of the three agree with each other and the arithmetic works, so we have described the machine as two 7.5 HP motors throughout this page. But we are not going to quietly delete the third figure and pretend the listing was clean. If motor sizing matters to your electrical design, your starter selection or your energy calculation, contact us and we will confirm the nameplate rating against the factory data before you order.

Will it fit, and will it run?

This is a 460V, 3-phase machine. That is the supply it needs, and there is no configuring around it — confirm your service before ordering, not after. Physically it is around 77 inches long and roughly 1,131 lbs, which puts it firmly in the category of equipment that needs a forklift, a properly rated slab and a planned route into the building. Do not plan on moving it a second time. The tank outlet is 1 inch. The listing also records an overall width and an overall height, but both are stored without a unit, so we are not going to publish them as measurements; ask us and we will send the dimensioned drawing rather than guess. Verifying floor loading, clearances, ventilation and electrical supply is the buyer's responsibility, and on a machine of this mass it is worth doing properly.

Perfect for

• Multi-bay shops that cannot lose air — where an unplanned compressor failure means sending technicians home.
• Production and fabrication floors running long, heavy demand cycles that suit a two-stage cast iron pump.
• Fleet and municipal workshops with maintenance schedules that need equipment serviceable without a shutdown.
• Operations planning on a long service life, where a rebuildable cast iron pump is a deliberate choice rather than an accident.

What is in the box

This listing states: two 7.5 HP motors and two solid cast iron two-stage pumps on a single 120 gallon ASME horizontal tank, plus the magnetic starter and the alternator. Air treatment is not included — there is no dryer here — and neither is downstream filtration, an automatic drain, isolation valves, interconnecting pipework or an electrical disconnect. Price those into the installation unless we have confirmed otherwise in writing.

Specifications

Approvals, stated plainly

The receiver is described as an ASME tank, and that is a real and useful statement about the pressure vessel. Beyond it, this listing makes no third-party approval claim — there is nothing here about the control gear or the assembly as a whole, and we are not going to imply one by leaving the subject vague. If your inspector, insurer or internal safety programme wants approval documentation covering the electrical package as well as the vessel, ask us before you order and we will request it from the manufacturer in writing. That is a much better conversation to have now than at commissioning, when the machine is already bolted down.

Shipping and delivery

Freight only, on a pallet, to the lower 48 states, with the cost quoted live at checkout so it reflects the actual lane on the day. Take the weight seriously when you plan receiving: about 1,131 lbs needs a forklift with the capacity to match, a dock, or a collection from the carrier's terminal where their equipment does the lifting. Residential delivery carries a residential fee, and on a machine this size a residential address is worth discussing with us before you order. Inspect before signing — walk both pump ends, look along the tank shell, check the starter enclosure and the pallet — and write anything you find on the bill of lading with the driver present. On heavy freight in particular, a note at delivery is what turns damage into a paid claim.

Warranty

This one is unusually clean and it is worth quoting as the listing puts it: a Two Year Full Warranty covering everything on the whole machine, with no fine print. Whole-machine cover for that term is not the norm on air compressors, and on a duplex it is doing double work, since there are two of everything to cover. The one thing that will undermine it is the same on every compressor we sell: do not disassemble a pump, a starter or the alternator before a claim has been opened. A machine that has already been taken apart is very hard to claim on, and the first question asked is always who opened it.