A vertical pump takes the same seal families as a horizontal one, usually a single cartridge seal, but the specification has to follow where the pump places the seal. On a vertical turbine pump the seal sits at the top of the column at full discharge pressure. That is also where air collects, and the long shaft below it moves sideways in service and lifts at every start.

When a seal on a vertical pump keeps failing, the cause is usually one of those conditions, and a seal specified as if the pump were horizontal allows for none of them.

Which Seal Type Vertical Pumps Use

Vertical pumps use the same seal types as horizontal pumps, and the usual choice is a single cartridge seal.

Cartridge Seals

Cartridge seals are the usual choice because they arrive preset and keep their compression setting through the impeller lift adjustments a vertical pump needs. A component seal has to be measured and set on the shaft in the field, and reset after each lift adjustment.

Split Seals

A split seal makes sense on a large vertical pump where fitting a solid seal means lifting the motor and uncoupling the shaft.

Single or Double Seals

A vertical pump needs a double seal when the pumped liquid or its vapour must not reach the atmosphere; for water and other harmless liquids a single seal is the norm. A double seal also suits a pumped liquid that is too dirty or too poor a lubricant for the faces.

Vertical sump and slurry pumps (API VS4 and VS5) on volatile or hazardous liquids are the clearest case, and they take a pressurized double seal with a liquid or gas barrier. A pressurized barrier on these pumps needs a drain port in the shaft column.

Seal Balance

A vertical pump needs a balanced seal when its seal chamber pressure is above 200 psi (1,380 kPa), and on a vertical turbine pump that chamber sits at the pump’s full discharge pressure.

The 200 psi figure is a rule of thumb, and each application is still reviewed for speed, temperature and the liquid.

A vertical sump pump’s chamber sits near atmospheric pressure, and a vertical overhung pump’s sits between suction and discharge, so on those pumps the balance decision is made as on a horizontal pump.

Flush Plan for a Vertical Pump Seal

Plan 13 is the usual flush plan for a vertical turbine pump seal, but other vertical pumps take other plans, because where the pump places the seal sets the pressure in the seal chamber:

  • Vertical turbine and wet-pit pumps (API VS1, VS2, VS3, VS6, VS7): seal at the top of the shaft column above the mounting plate, chamber at discharge pressure, Plan 13.
  • Vertical sump and slurry pumps (API VS4, VS5): chamber near atmospheric pressure, column full of air or vapour, a pressurized barrier on Plan 53, 54 or 74.
  • Vertical overhung pumps (API OH3, OH4, OH5): seal just above the back of the impeller, chamber between suction and discharge pressure, Plan 13, 14 or 32.

On a vertical turbine pump, size Plan 13 to give the faces enough flow to stay cool. If the liquid carries solids, add a bleed bushing, usually supplied by the pump maker, and a Plan 32 clean flush.

On a vertical overhung pump, choose the plan as on a horizontal overhung pump: by chamber pressure against suction pressure, and against the liquid’s vapour pressure. Use Plan 14 when chamber pressure sits only a little above the liquid’s vapour pressure.

Seal Materials for Vertical Pumps

In water service, choose the face pair by the solids the pump lifts and the elastomers by the water’s treatment chemistry. In process service both are chosen for the liquid, as on any pump.

Seal Faces

For clean water, carbon against ceramic is the standard pair; once sand reaches the faces, change to two hard faces, most often sintered silicon carbide against sintered silicon carbide. The wear on faces pulled from the well is the practical guide to when that change is due.

Tungsten carbide is the other hard face. It handles thermal stress better than silicon carbide, which can crack under it, but its nickel or cobalt binder can be leached out by aggressive chemicals. The thermal side matters on a vertical turbine pump that starts with an empty column, because the faces turn briefly without liquid until the water reaches the top.

Run dry, two carbide faces damage each other quickly, so a hard pair on a vertical pump depends on the venting described under Air in the Seal Chamber. Silicon carbide grades loaded with graphite ease that dry-running damage.

Elastomers

For plain cold water, nitrile (Buna-N) is the standard elastomer. EPDM is the water and steam choice where no oil or hydrocarbon is present, and FKM (Viton) covers higher temperatures and wider chemical service.

Chloraminated supply water changes the choice, because nitrile swells in it. Peroxide-cured EPDM is usually favoured there, but even EPDM swells badly if it is not compounded for it. Ask for a compound tested for chloramine resistance; ASTM D6284 is the test method.

Converting a Packed Vertical Pump to a Mechanical Seal

When packing is replaced with a seal, the packing box has to change, and three things need attention:

  • The chamber: fit an enlarged-bore seal chamber; a tapered bore also vents itself. On vertical in-line pumps, a chamber built to the ASME B73.2 standard dimensions takes standard seals.
  • The vent: fit a vent connection at the highest point of the chamber, because the seal stops the packing leakage that used to carry air out.
  • The shaft: check the sleeve surface where the seal’s elastomer will sit and, on lineshaft pumps, the lineshaft bushings.

What Vertical Mounting Does to the Seal

Vertical mounting exposes the seal to shaft deflection, axial shaft movement and trapped air. Deflection and axial movement come from long lineshafts, so they apply to vertical turbine, wet-pit and can pumps. Trapped air affects every vertically mounted seal, vertical overhung and multistage pumps included.

Shaft Deflection on Long Vertical Shafts

No standard figure says how much radial movement a seal can absorb, so the limit is set on the pump: shaft deflection at the seal faces of no more than 0.002 in total indicated reading (TIR) under the most severe operating condition.

Worn lineshaft or bowl bushings let the shaft move further at the seal, and the resulting vibration at the seal faces shortens seal life.

On the seal side, specify a cartridge seal with high radial clearance around the shaft, with enough flexibility in its own mounting to follow the movement that remains.

Axial Shaft Movement

A vertical turbine pump’s shaft moves up at every start, and the seal has to keep its faces together through that lift. Upthrust that lasts beyond the start often shows only as repeated seal failures, so a vertical turbine pump that keeps losing seals needs its thrust checked before a different seal is tried.

Air in the Seal Chamber

Air is kept off the faces of a vertically mounted seal by venting the top of the seal chamber continuously; venting it once before start-up is not enough. Flush water keeps carrying entrained air in, so a chamber vented only once builds an air pocket around the faces and the seal runs dry while the pump still delivers liquid.

Put the vent or flush-out port high, above the faces and as far outboard as possible, with the flush-in port below it. Tangential ports help the flow sweep the chamber.

Plan 13 on a vertical turbine pump and Plan 14 on a vertical overhung pump vent the chamber the whole time they run; where neither is fitted, a float-type air-release valve on the vent port does the same job. A double seal is the exception: the liquid between its seals is a closed barrier circuit that brings in no new air, so venting it when it is filled is enough.