Swivel joints in floating suctions and roof drains: what wears and how to look after them

A floating suction or articulated roof drain has only a few moving parts, and the swivel joints are the ones that do the work. Each joint turns every time the level changes, carries the weight of the arm and float, and must stay sealed against the product. When a floating suction stops following the level, a stiff or seized swivel is the usual cause.

At a glance

• What wears: seals, ball races and lubricant.

• Signs: the arm lags the level, the position indicator stops moving, product weeps from the joint.

• Check: at every tank cleaning or internal inspection.

• Fix: replace seals or swap the flanged joint.

How a swivel joint is built

Two body halves turn on hardened ball races. Seals keep product out of the bearing and stop leakage, and the races are packed with a grease that suits the product. Flanged ends let a joint be removed and replaced without cutting pipe.

What goes wrong

Symptom	Likely cause	What to do
Arm lags behind the level or sticks	Dry or contaminated bearing, corrosion, debris in the races	Free and inspect the joint; regrease or replace.
Position indicator stops moving	Seized joint, or the float has lost buoyancy	Check the joint and the floats together.
Product weeping from the joint	Worn or wrong seal material	Replace seals with a grade suited to the product.
Float sits low in the liquid	Leaking float, not the joint	Pressure test or replace the float.

What to check at each tank inspection

• Move the arm through its full swing by hand and feel for stiff spots.

• Look for product weeping at the seals and corrosion on the body.

• Check flange bolts and the stops that limit the arm.

• Check the floats for leaks and the pads that protect the tank lining.

• Confirm the position indicator follows the arm.

Aviation fuel

Swivels on jet fuel service use an aviation-grade grease, and grease nipples are replaced with stainless plugs. Use the same grade when servicing.

Vens supplies heavy duty swivel joints for floating suctions, articulated roof drains and loading arms, and can make joints to replace worn ones on existing assemblies when the dimensions are known. For a full maintenance routine see our floating suction maintenance guide.

Vens floating suction units are designed by engineers who studied at MIT, Stanford, Cornell, the Indian Institutes of Technology, Arizona State University and the University of Cincinnati, and who have worked in the refineries, depots and power plants that use them. They size each unit for the tank, the product and the duty, choose materials and seals for the product, and design to proper factors of safety.

Need a replacement joint? Send us your details or e-mail venshydro@gmail.com with the size, end connections and a photo of the existing joint.