YSM D Mark III vs Flowserve Durco Mark 3: What Is Interchangeable, What Is YSM’s Own Design

Quick answer: what “interchangeable with the Durco Mark 3” means on this page

The D Mark III is YSM’s B73.1 family built to the Durco Mark 3 dimensional pattern: General Purpose (26 sizes, Groups 1 to 3), Low Flow (4 sizes, Groups 1 and 2) and Unitized Self-Priming, a reverse-vane family made to YSM’s own drawings and patterns. “Interchangeable” has three levels here.

Level 1, installation fit. The ASME B73.1 scope covers mounting dimensions, nozzle size and location, input shaft, baseplate and foundation bolt holes for the same designation; that is what “built to the same ASME B73.1 envelope” means here, confirmed against the nameplate and the installed pump drawing before order.

Level 2, part and assembly fit. Casing-to-frame, impeller-to-shaft, cover-to-casing and seal-chamber geometry are the manufacturer’s own design; whether a YSM part mates with an installed OEM part is reviewed against the drawing and part number, never assumed from the group.

Level 3, hydraulic match. B73.1 is a dimensional and mechanical standard, not a performance specification (see ANSI/ASME B73.1 explained); the D Mark III size curve is compared with the duty point separately.

Reverse-vane impeller: how the Mark 3 pattern sets running clearance

Flowserve describes the Durco Mark 3 reverse-vane impeller as setting running clearance against the rear cover, adjusted externally.

The D Mark III follows the same principle: clearance is set between impeller and rear cover and adjusted at the bearing housing, and pump-out vanes are listed in YSM’s published description. The impeller is a YSM casting to a YSM drawing, not an OEM part. The G196 series (Goulds 3196 pattern) uses a front-clearance open impeller, so the two wet ends are not cross-compatible.

Flowserve also lists open (front-vane) and recessed impeller variants. For the D Mark III the reverse-vane impeller is standard; open impellers are available for part of the size range, confirmed per size at quotation; recessed impellers are not published.

When an impeller is reverse engineered from a sample or drawing, YSM digitises cast surfaces and vane profiles by 3D scanning or CMM, simulates the casting before pouring, uses 3D-printed sand cores or moulds and checks impeller hydraulics against the pump curve (see reverse engineering pump parts). No fixed clearance, runout or vibration limit is published, and clearance is set per size, temperature and drawing.

Group 1, 2 and 3: which sizes belong to which group

Flowserve publishes 30 Durco Mark 3 ASME sizes on three power frames (7 in Group 1, 16 in Group 2, 7 in Group 3, including four LF low-flow sizes); Mark 3 Group 4 for higher flows is outside the ASME dimensional scope. YSM publishes the same 30 strings as 26 general-purpose and 4 low-flow sizes; per-size availability is confirmed at quotation.

Durco and D Mark III size codes give suction size x discharge size, then nominal impeller diameter (3x2-13: 3 in suction, 2 in discharge, 13 in impeller); Goulds 3196 and G196 codes reverse the nozzles (2x3-13), so the B73.1 designation (AA to A120), not the string, is the comparison key.

The group decides the power end: bearing frame and housing D1119/D1201, D2119/D2201 and D3119/D3201 for Groups 1, 2 and 3; casing, impeller and cover are size-specific. OEM part-number cross-reference tables are on the replacement ANSI pump parts page.

Durco Group 2 spans more than one B73.1 designation, so mounting is compared by designation and general arrangement (GA) drawing, not by group. Flowserve publishes inboard 6310 and outboard 5310 bearings for its Group 2 power end; YSM’s bearing designations are not published and are confirmed on the sectional drawing.

Seal chamber variants: CBS, CBL, FMS, FML and the FMI question

Flowserve’s SealSentry chambers are integral with the rear cover in five designs (FML, FMS, FMI, CBL, CBS), with jacketed rear covers available. YSM publishes covers corresponding to the CBS, CBL, FMS and FML configurations (Flowserve designations, used for identification only) and a packed stuffing box; FMI-type seal chambers and jacketed rear covers are not offered.

The chamber is part of the rear cover, so the variant fixes the cover casting and is read from the seal drawing, order record or installed cover. Seal transfer is never automatic: the existing seal (make, model, cartridge or component, single or dual, flush plan, shaft type) is reviewed against the D Mark III chamber bore, depth and gland bolt pattern, because B73.1 fixes only the chamber envelope.

ANSI 3A vs Mark 3A, Mark II and Mark 3 ISO: what this page covers and what it does not

Flowserve’s ASME line uses the “ANSI 3A” power end, which Flowserve states conforms to ASME B73.1, and offers the “Mark 3A” power end where B73.1 compliance is not required.

“Mark 3” on a nameplate therefore does not say which power end is installed. On YSM’s parts cross-reference page, “Mark IIIA Group 1/2/3” identifies frames and bearing housings for Flowserve’s ANSI 3A (ASME B73.1) power end, not the non-B73.1 Mark 3A power end; fit is confirmed against the nameplate and the installed pump drawing before order. A Mark 3A installation is a different item, confirmed dimension by dimension against the D Mark III GA drawing before quotation.

Durco Mark II, an earlier pattern, and Mark 3 ISO pumps, built to ISO 2858 and ISO 5199 rather than B73.1, are outside the D Mark III scope and go to a separate review.

What is interchangeable and what is YSM’s own design

Items built to the same ASME B73.1 envelope are compared for the same size and designation, confirmed against the nameplate and the installed pump drawing before order. YSM-design items (casing, impeller, rear cover and seal chamber, adapter, bearing frame and housing, shaft, hook sleeve, feet) are produced to YSM’s own patterns and drawings and reviewed for fit against the drawing. Bought-out items are SKF or equivalent bearings, John Crane or equivalent mechanical seals and WEG or equivalent motors.

Mixed assemblies (a YSM wet end on an installed OEM power end, or the reverse) are quoted only after the interface dimensions on the installed pump drawing are reviewed; a part-number match alone does not confirm fit.

Durco Mark 3 dimensions: which figures to compare and where they come from

YSM publishes the D Mark III installation dimensions (Rev. A, 2026-07) and the lettered drawing on the technical downloads page.

The B73.1 designation (AA to A120), not the OEM group, fixes D, CP and the foot pattern, and the installed pump’s designation is confirmed on its certified GA drawing before order.

In the table: CP, coupling end to suction flange face; D, shaft centreline height above the underside of the feet; X, centreline to discharge flange face; 2E1 and 2E2, bolt-hole spacing across the shaft (0 means one hole on the centreline); F, spacing of the bolt-hole rows along the shaft; U, shaft diameter at the coupling; Y, discharge nozzle centreline to suction flange face; H, bolt-hole diameter.

The letters follow ASME B73.1; the D Mark III drawing on technical downloads dimensions E1 and E2 from the shaft centreline, half the full 2E1 and 2E2 spacings. A Durco size is placed in a designation only when its nozzle-reversed string is a Goulds 3196 size listed there (Durco 3x2-13 = Goulds 2x3-13 = A30), as Flowserve publishes no designation table; other sizes read “designation per certified drawing”.

Flange rating (Class 150 or 300), nozzle orientation, auxiliary connections and baseplate type are not decided by the size string, and nominal impeller size can vary by manufacturer, so the designation is verified on the certified drawing or by measurement. A size-specific GA drawing is available via the contact page.

Nameplate, drawing and fit checklist before a D Mark III order

Photograph both the pump and motor nameplates (see the nameplate and drawing guide); a nameplate cannot confirm current impeller trim, internal wear, wetted materials or part-to-part interchange. Add duty data (flow range, head, speed and Hz, liquid, temperature, SG, viscosity, solids, NPSHa) and any drawings or part numbers; see information needed before replacing an ANSI process pump and, for urgent parts, the urgent ANSI pump parts RFQ checklist.

Confirm before you order

1. Size string, group and serial number from the pump nameplate, with photographs of both plates.
2. Generation confirmed as Mark 3 ASME; Mark II and Mark 3 ISO go to a separate review.
3. Power-end type confirmed as ANSI 3A or Mark 3A; a Mark 3A power end is checked dimension by dimension against the drawing.
4. B73.1 designation, D, CP, foot pattern, flange class and nozzle orientation compared between the two GA drawings.
5. Seal-chamber type and the existing seal (make, model, flush plan, shaft type) checked against the D Mark III chamber geometry.
6. Coupling hub bore, spacer length, guard, motor frame and rotation confirmed on the GA drawing.
7. Duty point and current impeller trim compared with the D Mark III curve for the size.
8. Material code, liquid, temperature and concentration stated, so the alloy follows the duty, not a name.

How the D Mark III is made, tested and supplied

YSM casts and machines the D Mark III to its own patterns and drawings at a 3,000 m2 site in Zhuangzhuang Industrial Park, Boshan District, Zibo, operating since 2010 with about 35 staff (see the factory review).

The certifications and quality page publishes the inspection steps: material verification by spectrometer or chemical analysis per heat; hydrostatic test of pressure-containing parts; dimensional inspection of machined parts and ASME B73.1 interface dimensions against the drawing, with the in-house CMM (Tornado NCA10158) for interface and fit dimensions; dynamic balancing of all impellers; performance testing of complete pumps on YSM’s own factory test benches (water medium, to 9,000 m3/h, 6 bar, 250 kW), with the test curve supplied on request; and final inspection.

Witness testing at the factory and third-party inspection by SGS, Bureau Veritas or TÜV are available on request. Material certificates, balance reports and hydrostatic test reports are issued with the order; a dimensional inspection report can be issued with the order. Export packing is non-fumigation wooden export cases, with small parts in inner cartons.

Lead times, warranty, payment and Incoterms are published on the commercial terms page. There is no public price list; quotations follow a reviewed selection (see how to compare process pumps from multiple manufacturers).

The D Mark III may also be reviewed for installed Summit Clark 3 pumps of the same size and group, confirmed against the nameplate and the installed pump drawing before order (see D Mark III for Clark 3-pattern installations).

Next step: send nameplate photographs, duty data and any drawings or part numbers through the contact page for an interchange review. General questions are in the ANSI process pump FAQ.