why do I only get a small amount of water hot or cold from the single handle valve and can I replace the cartridge to correct.

I'm sorry that you are experiencing low flow! We would be happy to help. The most common cause of a low flow rate is debris. The best way to clear any debris is to flush the supply lines. To do this, turn off the water supplies, remove the cartridge, and turn the supplies back on for one minute. Please make sure that you are getting good flow through both the hot and cold side while flushing. You can also shake the cartridge back and forth to make sure the back half of the cartridge rattles. This means that the pressure balancing spool is moving freely, as it should. If it does not, you can try soaking the cartridge in white vinegar for about 15-30 minutes. For further assistance, please feel free to reach out as we would be glad to help. Best regards, Jon Phone: 1-800-345-3358 | Email: customerservice@deltafaucet.com | Facebook/Twitter: @deltafaucet