Class 300 Knife Gate Valves for the Pani Gold Project: 14 in, Built to MSS-SP-81

Knife gate valves are the most casual-looking valves in any plant — a thin blade, a bonnet, a wheel. The casualness ends at Class 300, in a 14-inch bore, in a gold plant that runs caustic cyanide solution through its process lines. This page describes a 14-inch Class 300 knife gate valve supplied for the Pani gold project of PT Merdeka Copper Gold, and what changes when a valve family normally bought as "cheap isolation" has to be engineered instead.

1. The duty, in six lines

Service: process water and slurry lines at a gold cyanidation plant — solutions bearing sodium cyanide and sodium hydroxide

Valve: 14 in knife gate valve, Class 300, RF flanged per ASME B16.5

Design and manufacture: MSS-SP-81 (face-to-face, end dimensions and body design all per this standard)

Body and bonnet: cast ASTM A351 CF3M; gate SS316L; stem ASTM A182 F316L

Operation: bevel gear, handwheel-mounted

Testing: shell 7.5 MPa, seat 5.5 MPa, per API 598

Everything else — the bolting, the packing, the seat — follows from these six lines.

2. Why Class 300 changes the knife gate

Most knife gate valves are bought in Class 125 or 150, where the standard's logic is simple: a thin wafer body, a blade, a seat. At Class 300 the arithmetic changes. The shell test pressure is 7.5 MPa and the seat test 5.5 MPa — roughly half as much again as the lower classes — and every part of the structure has to carry it: a beefier cast body around the gate cavity, a gland arrangement that stays tight at the higher load, flange bolting in 14 × Ø33 mm holes on a 514 mm flange face.

What does not change is the reason a knife gate was chosen at all: a straight-through bore with a thin blade gives the slurry a clear path when open and a clean cut when closing. A 14-inch gate valve or ball valve would do the isolation, but the knife gate does it in a fraction of the face-to-face (159 mm at this size) and at a fraction of the weight — 1,343 mm overall height with the bevel gear, against well over twice that for a bolted-bonnet gate valve with gearbox.

3. Where it sits in a gold plant

Cyanidation — dissolving gold from ore in dilute sodium cyanide solution, typically around 2 % w/v held at pH 11 with sodium hydroxide — runs the whole back end of a gold plant: leach tanks, transfer lines, process water headers. The valves on these lines face two simultaneous problems. The solution is corrosive to ordinary steel, and the lines carry solids that jam or erode anything with a narrow, obstructed flow path.

That combination — chemical resistance plus straight-through slurry flow — is exactly the knife gate's territory, and exactly why the materials matter as much as the pressure class here.

The purchase order also shows the scale of the phase this valve belongs to. The package covers more than five hundred line items and close to a thousand valves in total: roughly 540 floating ball valves, 170 butterfly valves, 135 dual-plate check valves, 116 knife gate valves, plus a small number of strainers. The list is not a random assortment — it repeats in identical blocks, one block per process line: three 14-inch Class 300 knife gates, one 8-inch Class 300 knife gate, three 14-inch ball check valves, nine 18-inch butterfly valves and a set of small-bore ball valves, line after line. Within each block, the knife gates are the smallest group by count and the most specific by duty. Every other valve in the block has a commodity equivalent on any distributor's shelf; the 14-inch Class 300 stainless knife gate — CF3M body, EPDM seat, bevel gear, tested at 7.5 MPa shell — had to be built to order against a drawing.

4. What the drawing fixed

The approved drawing locks the engineering in place before production starts:

Design, face-to-face and ends to MSS-SP-81 — the dedicated knife gate standard, which keeps the valve interchangeable with the plant's existing SP-81 line-ups

A cast body and bonnet in ASTM A351 CF3M — the cast 316L grade, confirmed at drawing stage

A bevel gear drive — at 14 inches, a plain handwheel on the gate stem asks for more torque than an operator should have to give; the bevel gear brings it back to a one-hand task and holds position against line vibration

5. Configuration matrix

6. Materials: what touches the solution

The fluid decides the materials list, line by line:

CF3M body and bonnet. The cast equivalent of 316L, with carbon held low for weldability and corrosion margin. Every wetted surface of the pressure boundary is austenitic stainless — there is no carbon steel in the solution path to be eaten by cyanide service.

SS316L gate. The blade slides in the seat every cycle; low-carbon 316L keeps corrosion initiated at the sliding edge from spreading, cycle after cycle.

EPDM seat. For this chemistry, EPDM is the right soft seat: it is close to indifferent to dilute caustic and cyanide solutions, where PTFE would be chemically fine but cold-flows under seat load. The trade-off is temperature and oil tolerance — which is why the seat choice is stated plainly in section 7 rather than buried.

Graphite packing. The stem packing is graphite, not rubber: the packing zone sees stem friction heat and needs to stay stable for years of infrequent but decisive operation.

B8M/8M bolting and a CF8M gland. Everything external in the wetted or washdown zone stays stainless as well, so a hose-down does not streak the valve with rust.

7. Where this valve is NOT the answer

Modulating service. A knife gate is an isolation valve. It is the wrong tool for throttling or control duty — the blade chatters against flow at partial openings.

Oil or hydrocarbon contact. The EPDM seat swells in hydrocarbons. Any line that can see oil contamination needs a different seat material — this is the one chemistry rule that overrides the otherwise excellent caustic/cyanide behavior.

Continuous hot service above the seat's comfort zone. The pressure boundary is rated −29 to 320 °C, but the EPDM seat's practical continuous limit is far lower. Hot lines need a metal-seated or high-temperature soft-seated design.

True double block and bleed. One resilient seat, one blade: fine isolation, but a plant that requires verified double isolation between live sections needs two valves or a DBB arrangement, not one knife gate.

8. Verification and document package

Each valve was hydrostatically tested per API 598 — shell at 7.5 MPa and seat at 5.5 MPa, the proof loads that correspond to Class 300 in this construction — with test records per valve. Material test certificates cover the cast body, bonnet, gate and stem; dimensional inspection confirms face-to-face and flange drilling to MSS-SP-81 and ASME B16.5 before shipment. The document package is assembled so the plant can file each valve against its line list, not sort loose certificates at site.

9. FAQ

Why specify Class 300 for a knife gate when Class 150 is the norm?

Because the line pressure dictated it. Knife gates in Class 300 carry roughly double the shell proof load of the lower classes; the body, gland and bolting are all sized for it. If the line runs at Class 150 pressures, buying Class 300 is paid weight; if the line is Class 300, a lower-class knife gate is a leak waiting for a test pack.

Is EPDM the right seat for cyanide and caustic solution?

For dilute NaCN and NaOH service, yes — EPDM resists both where many elastomers fail. The exceptions to state out loud: hydrocarbons (EPDM swells) and sustained high temperature. Where either appears, the seat material changes.

Why a bevel gear on a 14-inch knife gate?

Gate torque scales fast with bore and seat load. At 14 inches and Class 300, a plain handwheel needs real force to seat the blade; the bevel gear multiplies the operator's input and holds the gate position against vibration — at a modest cost in operating time.

Is the valve bi-directional?

The resilient-seated construction tolerates pressure from either side, but the gland and packing stack are optimized for the standard flow-to-seat orientation. Check the drawing for the preferred installation direction on high-pressure lines.

10. Send us these eight lines and we will quote

Fluid, state and chemistry (solution concentration, pH)

Line size and pressure class

Solids content or slurry description, if any

Operating and design temperature

End connection and face-to-face constraint

Operation: handwheel, gear, or actuated

Seat material preference or service restriction (oil contact? temperature?)

Applicable standards and testing requirements

Valve technical data on this page: approved shop drawing QM4043X-300LB (V02C) and purchase-order description, knife gate valves for a gold processing project.