Why a Progressive Cavity Pump Fits Slop Oil Injection
The application is continuous, slow injection of slop oil into a crude unit charge at 2 to 10 GPM, controlled by VFD speed rather than a flow meter, because trash in the slop plugs meters, orifice taps, and spillback valves. The temporary Watson-Marlow hose pump achieves roughly two months of hose life in this service. A progressive cavity (PC) pump is a positive displacement design whose flow is proportional to rotor speed, so RPM-based flow control works exactly as it does on the hose pump, and PC pumps are well suited to dirty fluids carrying solids. This preserves the existing control strategy — flow verified by tank level over time — while targeting a longer wear interval than the hose pump delivers.
PC Pump Selection Criteria That Drive Service Life
Speed is the dominant selection constraint: do not accept any PC pump selection with a running speed above 400 rpm. Low-speed operation is what delivers long stator and rotor life; a cheap high-speed pump is a known trap, because spare parts consumption over the following eighteen months can exceed the original purchase price. Specify the following in the enquiry:
- Maximum running speed of 400 rpm at the full 2–10 GPM turndown, not just at minimum flow.
- A mechanical seal explicitly rated for the slop oil duty.
- Hard-coated rotor/stator components where extended life is required; Mono Pumps has developed hard coatings for this purpose and offers a five-year component guarantee when it is specified in the enquiry.
- References from existing installations demonstrating long component life in comparable service.
Vendor Landscape for Refinery PC Pumps
The original question asked whether Roper at roughly half the price of Moyno is a case of “you get what you pay for.” The evidence does not compare those two brands directly; the decision path instead runs through the criteria above — a vendor willing to guarantee low-speed selection and component life is the meaningful price discriminator, not the nameplate.
| Vendor | Evidence-Backed Notes |
|---|---|
| Mono Pumps (owned by National Oilwell) | Cited as a field leader; hard coatings for extended life; five-year component guarantee available on request |
| Netzsch NEMO | Long history in oil and gas production, hydrocarbon treatment, tank storage, and refineries; applied to drilling muds, bentonite, oil muds, and oil-water mixtures with bulky particles — http://www.netzsch-pumps.com/e_allg/fr_anw.html |
| seepex | Recommended based on direct user experience — http://www.seepex.com |
| Discflo | Proposed as an additional candidate for this service — http://www.discflo.com/index.html |
Flow Measurement Options for Trash-Laden Slop Oil
Orifice taps get trashed, PD meter vanes get torn up, and coriolis tubes plug in this service, which is why flow is currently inferred from tank level over time. The obstruction-free alternative supported by the evidence is an electromagnetic (magflow) meter: no moving parts and no internal obstructions, provided the fluid is conductive. Install it in a vertical pipe run with upward flow so the tube stays full and solids do not settle. Krohne magflow meters have been used in slurry service containing 75% solids, including custody transfer duty, which is far more demanding than slop injection. Because slop conductivity is unverified in the evidence, de-risk the purchase by trialing a unit on a rental or “no cure, no pay” basis before committing; ABB is one supplier named for such meters (http://www.abb.com).
Frequently Asked Questions
What is the maximum recommended speed for a progressive cavity pump?
Do not exceed 400 rpm in any PC pump selection. Low-speed running is what produces long stator and rotor life; a cheap high-speed pump typically costs more in spares over the next eighteen months than the original purchase price.
Can a flow meter survive slop oil service with trash and solids?
An electromagnetic flowmeter has no moving parts and no internal obstructions, so it tolerates solids that destroy orifice taps, PD vanes, and coriolis tubes. Install it in vertical piping with upward flow, and verify fluid conductivity on a rental trial before purchase.
Which progressive cavity pump vendors serve refinery slop service?
Mono Pumps (owned by National Oilwell) offers hard-coated components and a five-year guarantee when specified; Netzsch NEMO pumps are established in refinery and hydrocarbon applications; seepex and Discflo are additional user-recommended candidates. Require long-life references and a 400 rpm speed limit from whichever vendor you select.