Does anyone know how to wash Wheelchair cover over cushion?

I would hand wash the cover and air dry until just a little damp and put back on the cushion so it does not shrink.

my mom's was polyester and I hand washed it. It took little time to dry. I will tell you that we made a new cover that was machine washable (with cotton in it) because the polyester made her "nether regions" sweaty!

See if you can get someone to sew you 2 new ones made out of a soft 100% cotton wasable fabric. I did this for my mom and mother in law. One to be on the cushion and another to change when one is being laundered. If you are feeling crafty, go to the fabric store. Purchase the fabric of your choice, washable, of course, and buy enough to cut 2 squares. Also buy velcro by the yard. Also purchase fabric glue. Take your cushion to use as a guide. Glue the velcro on all 4 sides, one on top and one on bottom. Instant new sew cushion covers that can instantly be changed out to launder. I found a nice cotton flannel for winter and a lovely no shed, low pile terry cloth for summer. Hope I explained well enough to understand.

I would wash the cover by hand in warm to cool water, very gently (often, these covers are surprisingly cheaply made, and will begin to unravel from the inside seams after laundering, sad to say) My friend who also has limited arm mobility has covered her cushions with an inexpensive bath towel, her assistant folded the bottom two thirds or so up and stitched the sides together, creating an open envelope she can just slip the cushion in. She drops the cushion in, folds the flap down and puts it in her chair with the opening down... looks great, and she has a nice clean cushion every day.

I washed both my Mother and Father's cushions from their wheel chair's in luke warm water on the delicate cycle . I used my regular laundry detergent that does not contain bleach. This worked great for me . Because of the urine odour I pre soaked in Lestoil (recommended by the nursing home). I think I mixed it quarter cup Lestoil to eight cups water. Hang to dry.

Yes you could use a pillow sham you could also just fold a towel to fit your seat, both are good ideas.