Obsessively Perfect

After years of witnessing Common to extreme wears on Rain Caps during repair, maintenance, or new customer requests, our field notes coupled with being one of the world’s foremost producers of caps have aided in our growth. The Parker team then takes back to the shop engineers all of the data from back pressure to weight ratios etc. to solve all the failure issues  encountered with our customers.  We are now stocking vertical exhaust rain covers from 3″ to 60″.


Read on for detailed engineering solutions built into our exhaust weather covers.

stocked for same day shipment

RainCap Design 2.0 

The infared analysis at left shows a 5 ft long exhaust stack with a rain cap at 45 deg in a 10 knot wind from the right. Note the eddy currents and back flow down the stack on the leeward side. Showing the exhaust fumes problematically swirling back toward the enclosure or into ground level surrounding areas.  Complex fluid dynamics calculations, weight distribution and balance forces have all be calculated to furnish your pipes with the most effective rain cap on the market.r

Kinematic Points

Most of us would say that they pivot point balances better. Our engineers said that the counter weight center of gravity and the lid center of gravity are optimized by placing them below the pivot axis instead of on the same plane.  In general market rain cap products you experience a design fault as the cap closes, it’s closing force declines to zero.  Maybe that’s not a problem if no wind blows in your rainstorms, but for our detail oriented engineers it’s a dual problem as it means the other rain caps don’t open past 50 or 60 degrees.  Our ran cover counterweight in the near vertical position of 70 to 80 degrees rests effortlessly below the pivot point.  The multiplied force of the center of gravity and the counter weight keep a solid weather protective seal when closed.

Open Fluid Dynamics

Most competitor rain caps only open about 60 degrees leaving the cap obstructing ~60% of the flow opening leading to the issues shown in the previous CFD analysis. The Parker rain cap opens to 80 degrees allowing for least obstruction in the market ~15% or less of the stack opening.  We alleviate flow and back pressure issues caused by less advanced caps.  The optimization lowered the overall weight and minimized the dynamic weight (inertia) of the lid when in motion while actually increasing the strength of the complete assembly.

  • 48% reduction in overall weight

  • 42% reduction in rotating inertia

Damage Resistant

The reduction in rotating inertia & the greater opening angle, with a conical lid geometry for strength our designs prevent deformation and/or metal separation during a backfire event. In a backfire event force the lower rotating inertia reduces the possible force applied when the lid reaches the opening stop point. The lower impact force reduces the chance of overall damage or lid deformation causing loss of function or cap separation from the stack.

The larger opening angle also reduces the impact force at the opening stop point during a backfire event through the 60% improvement in exit volume. The backfire force has less surface area to act on and a decreased force vector angle. The VER2.0 designed conical shape of the lid prevents suction forces “concave bending” a cap during a backfire event.  We all understand the loss of function and possible engine water damage possible in a remote or un-monitored location.  Installing a flat cap or lesser functional design may leave your backup generator stalled or damaged upon start.

Zen balance

The counter weight CG and lid CG were optimized by placing them below the pivot axis instead of on the same plane as the pivot axis. With most other product, the closing force approaches zero as the lid opening angle approaches 90 deg, therefore the lids only open to a smaller angle in order to maintain a closing force.

closing force

With the new design, at 70 deg, the counterweight CG is directly below the pivot axis, therefore from 70 to 80 degrees, both the lid CG and ounterweight CG work in an additive function, increasing closing force as the lid approaches 90 deg. This allows for the greater opening angles without compromising closing force.

custom specs available

We customize rain cap features, such as customer defined lift off or closing pressure values to perfectly adapt to your needs and environment. Engineering will custom design rain caps to any special customer requirements including specific pressure, diameter, or durability requirements.

Opens when needed

Bronze Bearings

Parker Fabrication Rain Caps use bronze top hat bearings to manage friction and provide weather resistance.  Designed to manage and absorb radial and axial load forces for clean opening on startup.  The engineering that lowered the overall weight by 48% and reduced the rotating inertia by 42% extend the service period and minimize wear even in adverse weather.

Stainless Steel Axle

The pivot rod manufactured from stainless steel prevents corrosion and ensures continued fluid lid opening motion.  All in all we have engineered and tested this small yet critical appliance for your genset resulting in an optimized raincap design. 

Covering Gensets Across the Globe