UI that are open on the client side send a regular heartbeat to the server to indicate they are still alive, even though there is no ongoing user interaction. When the server does not receive a valid heartbeat for a given UI, it will eventually remove that UI from the session.

By default, heartbeats are sent every five minutes, and the server closes an UI after three missed heartbeats.

This is done in the web.xml by setting the heartbeatInterval value

  <context-param>
    <param-name>heartbeatInterval</param-name>
    <param-value>90</param-value>
  </context-param>

https://vaadin.com/book/vaadin7/-/page/application.lifecycle.html