Summary

Variable volume tank lids use an inflatable rubber gasket to create an airtight seal between the floating lid and the tank wall. The gasket is inflated with a small hand pump and works similarly to a bicycle tire tube.

If your tank is losing pressure or the gasket will not stay inflated, the issue is usually caused by:

• A leak in the inflatable gasket

• A leak in the pump or pump seals

• A loose connection in the tubing

This guide explains how to locate the source of the leak and determine whether you need to replace the gasket, repair the pump, or install new seals.

How Variable Volume Lid Gaskets Work

Variable volume tank gaskets inflate outward to press against the inside wall of the tank, forming a seal that protects wine from oxygen exposure. Because the gasket relies on air pressure to maintain the seal, any small air leak can cause the gasket to slowly deflate.

Identify Where the Air Leak Is Coming From

Before replacing parts, determine whether the leak is in the gasket or the pump system.

Method 1: Submerge the Gasket

1. Inflate the gasket.

2. Submerge it in water (a sink, tub, or large container).

3. Look for streams of bubbles, which indicate the leak location.

Method 2: Spray Test

1. Inflate the gasket normally.

2. Spray the following solution over the gasket:

   • Mild soapy water, or

   • Star San solution

3. Watch for bubbles forming, which reveal where air is escaping.

If bubbles appear on the gasket itself, it obviously needs replacement. 

If no bubbles appear on the gasket, the pump seals or connections may be the issue.

Check the Pump for Leaks

Leaks often occur inside the hand pump assembly rather than the gasket.

Over time, the pump’s internal seals can:

• Wear down

• Warp

• Dry out

When this happens, the pump may slowly release air even though the gasket itself is intact.

In many cases, replacing the pump seal kit restores normal operation. If replacing the seals does not resolve the issue, the entire pump assembly may need replacement.

Replacement pump seals and kits are available for both Marchisio and Speidel variable volume tanks.

Isolate the Pump to Diagnose the Leak

If you'd like further assurance the leak is coming from the pump, you can isolate the pump using a simple valve.

What You Need

• ⅜” x ⅜” barb inline ball valve

• Hose clamps

These parts are commonly available at most hardware stores.

Installation Steps

1. Cut the air tubing between the pump and gasket.

2. Insert the inline ball valve between the two hose ends.

3. Secure the connections with hose clamps.

How This Helps

After inflating the gasket:

• Close the valve.

If the gasket stays inflated, the leak is likely in the pump.

If the gasket still loses pressure, the leak is likely in the gasket itself.

This simple test helps determine which part needs to be replaced.

Replacement pumps are available for both Marchisio and Speidel variable volume tanks.

When to Replace the Gasket

Replace the inflatable gasket if:

• Visible bubbles appear along the rubber tube

• The gasket will not hold air even after pump repairs

• The rubber shows cracks, dry rot, or wear

Replacement gaskets are available for both Marchisio and Speidel variable volume tanks.

Quick Troubleshooting Guide

Tips for Maintaining Your Tank Gasket

• Avoid over-inflating the gasket

• Keep the gasket clean and free of debris

• Store tanks in moderate temperatures

• Periodically inspect the pump seals

Regular inspection can help prevent leaks and ensure your variable volume tank maintains a proper seal.