Opella Delcham Multiflush Oval Cistern Syphon, 7 1/2 inch x 1 1/2 BSP


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How the Dual Flush operation for this siphon works.

The full flush volume is achieved by flushing the WC in the normal fashion of fully depressing the lever and immediately releasing once the flush has started. The short flush volume is achieved by fully depressing the handle in the normal fashion and holding the handle in the down position until the flushing cycle has finished

Internal Overflow

If in the unlikely event that your filling valve fails to open, all Opella siphons feature an internal overflow which will be able to cope with up to 35l/mm of excess water. As the water level rises so will the level of water within the siphon, until it reaches the 'Spillover' point. At this point the water within the siphon will cascade down the down tube and into the pan preventing any further increase in the height of the water within the cistern. When choosing an Opella siphon please make sure the bottom of the coloured cap (the Spillover’ point, point P) is lower than any existing exit point within the cistern, i.e. lever handle / side lever / side inlet internal overflow and cistern rim.

cistern spillover

What should I do before starting work?

Keep children away from the work area.

Always wear use suitable protective equipment when using tools.


WARNING: Solder flux and some seating compounds can damage this plastic plumbing product.

Fitting the Dual Flush Siphon

STAGE 1 Pre Installation

  1. Turn off water supply to cistern and remove cistern lid.
  2. While still full. mat-k the normal water level on the inside of the cistern.
  3. Flush flit cistern and remove all remaining water with a sponge or cloth.
  4. Disconnect the t link from the flushing lever and save for use again if required.
  5. Remove old siphon.


Fitting the Delchem Dual flush Siphon For high and Low Level cisterns

  1. Undo the coupling nut below the cistern and undo the siphon backnut.
  2. Take the old siphon unit out of the cistern and fit new siphon ensuring that the rubber washer is On the inside of the cistern.
  3. Hand tighten the backnut and tighten a further quarter of a turn using suitable grips.
  4. Refit the ‘C’ link.
  5. Refit the flush-pipe sealing washer and coupling nut.

For close coupled cisterns

  1. Disconnect the water supply from the tailpipe of the filling valve.
  2. Undo the wing nuts at the rear of the WC pan, undo the watt fixing screws inside the cistern.
  3. Carefully lift the cistern from the WC pan.
  4. Remove the large ‘doughnut’ shaped washer, then undo the siphon backout.
  5. Take the old siphon unit out of the cistern during which it may be necessary to remove some or all of the filling valve assembly.
  6. Fit the new siphon into the cistern ensuring that the rubber washer is on the inside of the cistern.
  7. Hand tighten the backnut and tighten a further quarter of a turn using suitable grips.
  8. Place a new doughnut washer on the thread and carefully reposition the cistern on the WC pan.
  9. Replace the wall fixing screws and the wing nuts.
  10. Refit the ‘C’ link.
  11. Reconnect the water supply to the filling valve.
Siphon Flushing Volumes (Indicative volumes only)
6 litres 7 litres 9 litres
dot dot dot
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Opella Delcham Multiflush Oval Cistern Syphon - 7.5 inch / 1 1/2 BSP

  • 6/7/9 litre convertible syphon
  • Size from thread side of flange to top welded seem: 8 inch
  • Outlet: 1 1/2 BSP (actual outside diameter: 47mm (1 3/4 in approx))

Please Note:

  • New installations: (cistern pan installed from 1 Jan 2001). To meet new water regulations the cistern should be set to flush 6 litres.
  • Replacement cistern: (connected to 7 litre WC Pan installed after 1 Jan 1993). Syphon should be set to 7litre (remove lower of two plugs).
  • Replacement cistern: (connected to 9litre WC pan installed before 1 Jan 1993). Syphon should be set to 9 litres (no plugs removed)


  • 6 litre flushing should only be used with WC pans specifically designed for a 6 litre volume.

Typical example of how set the syphon for various flush capacities.


Category: Syphons

Product Details

  • Our Code: 5011629001410
  • Shipping Weight: 0.3Kgs
  • 0 Units in Stock
  • Manufactured by: Opella

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Date First Available: Wednesday 01 June, 2011.

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