Introduction
Filling hatches — the upper loading covers on the crown of the silo barrel — are the point through which a Feldbinder silo trailer receives bulk material. Every hatch must be securely closed for transport and for pressurised discharge. That closure is provided by wing bolts: complete galvanised steel assemblies that are tightened by hand via the eye, pressing the cover firmly against the hatch gasket.
On Feldbinder silo trailers — both the horizontal, non-tipping EUT and the tipping KIP — a positive hatch closure is essential for pressure integrity. A loose or damaged wing bolt creates the risk of a leaking hatch and pressure loss during discharge, and on food-grade tankers also the risk of cargo contamination. Wing bolts are a service-wear item, susceptible to thread wear and corrosion, which is why we treat complete wing bolt sets as a standard stock line.
PHS Magnum in Chorula near Opole supplies complete wing bolts, eye bolts, and brass retaining clips for Feldbinder filling hatches.
Specification and Materials
Complete wing bolt assemblies for filling hatches:
| Property | Specification |
|---|---|
| Material | hot-dip galvanised steel |
| Eye diameter | 18 mm |
| Type | wing bolt (complete assembly) |
Also available:
- Eye bolts to match the above wing nuts — all sizes, in stainless or galvanised steel.
- Brass retaining clips.
Sizes and Types
Full size range of wing bolts. For Feldbinder silo trailers the reference sizes are:
- M20x100
- M20x120
- M20x130
All with 18 mm eye, in hot-dip galvanised steel. Other sizes and finishes available on request.
Compatibility with Feldbinder Silo Trailers (EUT/KIP)
- EUT — wing bolts close the upper filling hatches on the horizontal barrel; a positive closure is a prerequisite for a pressure-tight seal during pneumatic discharge.
- KIP — the same filling hatches are present on the tipping silo; secure closure is equally critical during tipping and pressurised discharge.
M20 wing bolts with an 18 mm eye fit Feldbinder filling hatches regardless of trailer type; the correct length is matched to the specific hatch.
Role in Silo Pressure Integrity
Closing a filling hatch is not merely about preventing it from opening in transit. The wing bolt presses the cover against the hatch gasket — and it is that clamping force that determines whether the hatch remains airtight under discharge pressure. If the clamping is insufficient (corroded thread, worn eye, wrong bolt length), the gasket will not seal correctly and the hatch will leak.
On Feldbinder silo trailers this links two categories of parts into a single functional assembly:
- Wing bolt — the clamping element, subject to corrosion and thread wear; a replaceable wear part.
- Filling hatch gasket — the sealing element, covered in a separate category; also a wear part.
For that reason, when servicing filling hatches we assess both components together: a new gasket on a worn bolt that will not tighten fully will not seal, and a good bolt on a hardened gasket will not seal either. Brass retaining clips complete the assembly by stabilising the closed position. For Feldbinder we supply bolts in sizes M20x100, M20x120 and M20x130 with an 18 mm eye.
Common Failure Modes
- Thread corrosion — zinc coating damaged by road salt; the bolt is difficult to tighten, risk of incomplete closure. Replace the complete set.
- Worn 18 mm eye — a deformed eye makes it impossible to tighten with confidence; replace the bolt.
- Missing retaining clip — without the brass clip the assembly holds the closure less reliably; fit brass retaining clips to complete the set.
- Wrong M20 length — a bolt that is too short or too long will not close the hatch correctly; select M20x100/120/130 to match the specific Feldbinder hatch.
Availability and Delivery
We hold stock of wing bolts and eye bolts at our warehouse in Chorula near Opole (4 km from the A4 motorway, approximately 180 km from the German border). Common M20 sizes and brass retaining clips are typically available from stock.
Delivery by courier throughout Poland and the EU; combined orders with hatch gaskets and other parts are welcome. For pricing — ask for a quote.
Related Categories
- Loading Hatch Gaskets — Elastomer seals for the top loading hatches of Feldbinder silos.
- Rear Hatch Closing Bolts — Closing bolts for the rear inspection hatch of Feldbinder KIP silos.
- Feldbinder EUT Parts — full range of spare parts for the horizontal silo trailer.
- Feldbinder KIP Parts — hydraulics and seals for the tipping silo.
- See also: spare parts hub, PHS Magnum silo trailer service.
See also: This category in the full PHS Magnum network catalogue (all makes) →
Author: Aleksy Pasternak — Managing Partner, PHS Magnum, 20 years in the industry, ISO 9001:2015 internal auditor (DEKRA).
